Base64 encoding is an easy binary-to-text encoding scheme. Because you can generally rely on the same 64 characters being present in many character sets, and you can be reasonably confident that your data's going to end up on the other side of the wire uncorrupted. available, see the BENCHMARKS file available in the source code), The trick involves the fact that a switch-statement may legally cross into Two equals sign at the end show that 4 zeroes were added (helps in decoding). Base64 encoding schemes are commonly used when there is a need to encode binary data, especially . *pos++ = (block[1] << 4) | (block[2] >> 2); Base64 encoding encodes any binary data or non-ASCII text data to printable ASCII format so that it can be safely transmitted over any communication channel. Work fast with our official CLI. This ostream base64-encodes all data written to it and forwards it to a connected ostream. pos = out = os_malloc(olen); Use Git or checkout with SVN using the web URL. System.Text.Json provides two ways to build a JSON DOM: JsonDocument provides the ability to build a read-only DOM by using Utf8JsonReader. size_t *out_len) return NULL; email. To expand a bit on what Brad is saying: many transport mechanisms for email and Usenet and other ways of moving data are not "8 bit clean", which means that characters outside the standard ascii character set might be mangled in transit - for instance, 0x0D might be seen as a carriage return, and turned into a carriage return and line feed. After deobfuscating the script, we got the following code: Figure 9 Deobfuscated GuLoader PowerShell script. } The ostream's state is therefore not updated to match the buffer's state. In the earlier version described at the end of 2022, the shellcode was stored inside the VBScript. In this article, you'll learn how to encode a string to Base64 encoded format. In all cases, the exception handler also checks the status of the debug registers: Figure 17 Checking debug registers in VEH. libb64: Base64 Encoding/Decoding Routines, http://www.chiark.greenend.org.uk/~sgtatham/coroutines.html, https://sourceforge.net/projects/libb64/files, http://sourceforge.net/cvs/?group_id=152942, http://creativecommons.org/licenses/publicdomain/, , Enumerating installed software, using the MsiEnumProductsA and MsiGetProductInfoA. pos = out; We will not describe this variant in detail, as it was already analyzed in the article GuLoader: The NSIS Vantage Point. Go contains a package called "encoding/base64" that has various functions to Base64 encode a sequence of bytes and also decode a Base64 encoded string. for (i = 0; i < len; i++) { For example, if you want to hide "comments" from a db administrator, then base64 is suitable for the job. Powers of two are natural bases for binary. Python has a module called base64 that contains functions to Base64 encode a sequence of bytes and also decode it back to a string. This will only build the Applies to: Base64 is a binary-to-text encoding scheme. where each byte is represented by 3 bytes. Starting from position 2, taking every third character from this string gives us a string that is another PowerShell script: Figure 7 GuLoader PowerShell script after removing the first layer of obfuscation. base64 contains: 26 Uppercase alphabets i.e., A,B,C,D,.Z. *pos++ = '='; Hexadecimal: store the bytes as hex pairs: AC 47 0D 1A etc. By continuing to visit this website you agree to our use of cookies. So to get around this, people encode the binary data into characters. "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; The GuLoader developers continually improve the anti-analysis and anti-debugging techniques. Two nibbles make 8 bits which are also called 1 byte. @CholthiPaulTtiopic: The results of encryption or compression, or sound/images/video. *pos++ = '\n'; After converting to binary format, divide binary data into chunks of 6-bits. The latest release is An example of this "license" is the Creative Commons Public Domain License, a if (line_len) GuLoader is one of the most prominent services cybercriminals use to evade antivirus detection. Contribute to gofer/libbase64 development by creating an account on GitHub. if (pad) { Add pad character if zero bits are added at the end of the input. *pos++ = base64_table[in[0] >> 2]; code for standalone encoding and decoding executables. =) to make it multiple of 3. The string $Parrotb is converted in the same way. }. To see how the jump address is calculated, lets look at the VEH code. A test file that can be used with a Google test suite (. I sometimes use it to pass JSON data around from one site to another, store information PHP - What is the real use of base64_encode function. | Finally, we will get the encoded version of our input string. The obvious problem with any such routine is the static keyword. Each Base64 character encodes 6 bits (except the last non-pad character which can encode 2, 4 or 6 bits; and final pad characters, if any). The following example specifies that the output is URL-safe. } Aside from what's already been said, two very common uses that have not been listed are. This function doesn't add any new line characters. tmp = dtable[src[i]]; C++ wrappers are included, as well as the source Learn how to Base64 Encode binary data in PHP. Tatham: Youwill discover the reasons for this below in our report. MD5 generates a 128-bit output which is represented using a sequence of 32 hexadecimal digits, which in turn are 32*4=128 bits. count++; In addition to code encryption, GuLoader utilizes many other techniques including anti-debugging and sandbox evasion techniques. code is rare; I couldn't pass up the chance. The obvious solution would be to wrap the state along Now we can see that the script allocates 2 memory areas, downloads the data from the link to Google Drive, and saves it to a temporary file %APPDATA%\Umig.For. In this article, you'll learn how to Base64 encode a string in Python. Point to be noted : One padding bit equals two zeroes 00 so two padding bit equals four zeroes 0000. Each base64 digit represents exactly 6 bits of data. If we dont take this into account, we can only decrypt the first 843 bytes of the downloaded payload, and the rest of the data will be broken. Lets see an example to understand the Base64 encoding process: Step 1: Organize the input into 24-bit groups (having four 6-bit groups each). Encryption keys and encrypted data are often stored in configuration and XML files where you cannot store the raw bytes. Both of these functions encode data as Base 64 and return the encoded string as a. Does the policy change for AI-generated content affect users who (want to) Why do we need to base64 encode images before transmitting? Download | A list of at least some protocols which would fail would be nice to have if someone knows. base64 executable, putting it in the relevant build directory. Some of our partners may process your data as a part of their legitimate business interest without asking for consent. Now let's dive into how BASE64 encoding works. Chris Venter : chris.venter[anti-spam]gmail.com : (U+000D) followed by a line feed character (U+000A). . The first 64 bytes of the downloaded data are skipped. If nothing happens, download GitHub Desktop and try again. * Caller is responsible for freeing the returned buffer. Base64 is used to encode binary files such as images within scripts, to avoid depending on external files. Depends upon your OS. The friends email software will Base64-decode the above encoded textual data to restore the original binary image. section at the bottom of this page. What is the command to get the wifi name of a BSSID device in Kali Linux? Anyone can convert the Base64 string back to its original bytes, so it should not be used as a means for protecting data, only as a format to display or store raw bytes more easily. However, in parallel with the ongoing development of antivirus software by cybersecurity vendors, the GuLoader developers also continued improving their product. This technique was first described in the article Malware Analysis: GuLoader Dissection Reveals New Anti-Analysis Techniques and Code Injection Redundancy. In GuLoader, the registered VEH is called in this case. Unlike the VBS variant, samples based on the NSIS contain the GuLoader shellcode, albeit in encrypted form. The latest version integrates new anti-analysis techniques, which results in . The first 654 bytes of the decoded data are placed in the first memory area ($Gamme2483 in the example), and the rest in the second ($Nulstille in the example). 97= 01100001, 99= 01100011, 101= 01100101, 011000= 24, 010110= 22, 001101= 13, 100101= 37. Packing and crypting services are specifically designed to resist analysis. routine even clearer. } What is needed is a structure for storing these variables, which is passed to *pos++ = base64_table[((in[0] & 0x03) << 4) | /** sub-blocks. Can be used to embed raw image data into a CSS property such as background-image. We can already see that the script code contains the URL pointing to Google Drive. This codes are licensed by New BSD License. Encode function is in namespace Base64. Base64 is sometimes used to embed binary data in an XML file, using a syntax similar to e.g. You have the following points to take note of: Strings stored in the database wont be human readable (You could sell that as a feature that database strings use a basic form of encryption). Unpack the tarball somewhere and change into the directory. application (see the To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Base64 has 33% overhead (for the price of safety. Checking if the hypervisor bit is enabled, using CPUID instruction (, Measuring time, using RDTSC in combination with CPUID (. In this article, you'll learn how to Base64 Encode a String in Node.js. c base64 Share Follow The last chunk of input contains exactly 8 bits: Four zero bits are added to form two 6-bit groups. olen++; /* nul termination */ if (line_len >= 72) { Lets consider a sample with SHA256 5fcfdf0e241a0347f9ff9caa897649e7fe8f25757b39c61afddbe288202696d5. The strings are decrypted using an XOR operation with the decryption key. This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository. After decrypting the strings, we can find a string that looks like a URL, but without a schema: Its obvious that the GuLoader authors realized the way the research community managed to decrypt URLs in the previous versions of the shellcode using the strings http:// or https:// in the known-plaintext attack to detect the first bytes of the decryption key. String to be encoded : abcd Length=4, it's not multiple of 3. (Still today, all characters set in the range 80-FF are non-standard). Encryption means nothing more than converting one string of data to another string of data that can be either later decrypted or not, and that's what base64 does. Please Sections: We should note that at the time of writing this article, it has been 3 weeks since the specified sample was uploaded to VT, and the URLs for both downloading the GuLoader shellcode and for downloading the malicious payload (Remcos) were still active: Lets take a look inside the GuLoader VBScript. They are all the same except for the last two characters and line ending requirements. Solving the Endgame. #include "includes.h" If any hardware breakpoints are set, the exception handler refers to the zero address instead of the ContextRecord address. Therefore, the result for the command $Tjene0 = Gothites9 OIUlEDiXSa ; is IEX . count++; The result looks something like "TWFuIGlzIGRpc3Rpb". modified in transit through systems, such as email, which were Base64 can be used in a variety of contexts: Base64 is often used as a quick but insecure shortcut to obscure secrets without incurring the overhead of cryptographic key management. Use Git or checkout with SVN using the web URL. The base64 is a binary to a text encoding scheme that represents binary data in an ASCII string format. in cookies about a user. return NULL; Ask Question Asked 14 years, 6 months ago Modified 1 year, 4 months ago Viewed 388k times 159 I have binary data in an unsigned char variable. Count the number of characters in a String. Wikipedia is a reasonably good source of more information. The term Base64 refers to a specific MIME content transfer encoding. The payload decryption algorithm itself has not changed in comparison to the previous GuLoader versions. The code chunks in the GuLoader shellcode are always different; various combinations of registers can be used. References | /* Invalid padding */ Could you tell me what this message means and what to do to let my Ubuntu boots? Always call close() when done writing data, to ensure proper completion of the encoding operation. What is it used for? A distinguishing feature of GuLoader is that the encrypted payload is uploaded to a remote server. rather than "Gaudeamus igitur, *dum iuvenes* sumus!"? } os_memset(dtable, 0x80, 256); If we choose to decide 8 char long output, it occupies only 8 bytes whereas it was occupying 16 bytes for 128-bit hash output. Because line breaks are considered white-space characters in a base-64 encoding, they are ignored when converting a base-64 encoded string back to a byte . return out; 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. If it is not multiple of 3 pad with special character i.e., = to } for (i = 0; i < len; i++) { Each of the three 6-bit groups is converted to the corresponding Base64 alphabet. resulting libb64-xxx directory and run make. if (end - in) { So "HELLO" is stored like this: Now lets dive into how BASE64 encoding works. When you have some binary data that you want to ship across a network, you generally don't do it by just streaming the bits and bytes over the wire in a raw format. A distinctive feature of the new version is that the encrypted shellcode is hosted on a cloud service (usually Google Drive). As you might expect, there are 64 total characters that go into the tale. } * Base64 encoding/decoding (RFC1341) Like other parts of the code, VEH code is obfuscated. end = src + len; Essentially each 6 bits of the input is encoded in a 64-character alphabet. if (count == 4) { Change each decimal to 8-bit binary representation. Does any body have any idea? It is also used as a generic term for any similar encoding scheme that Special characters could be a use case but why not utf8 in that case, are they equibalent? this method, can be found in the above mentioned "Coroutines in C", by Simon # include < iostream > # include < base64.hpp > int main . I am thankful for the following contributions to this libary. Hiding the main thread from the debugger calling the NtSetInformationThread function with the ThreadHideFromDebugger (. When the input has fewer than 24 bits at the end, zero bits are added (on the right) to form an integral number of 6-bit groups. GuLoader is aprominent shellcode-based downloader that has been used in a large number of attacks to deliver a wide range ofthe most wantedmalware. https://sourceforge.net/projects/libb64/files routine (the callee). What is Base64 Encoding. This is an excellent point of discussion and an interesting history lesson, thanks. Many thanks to Read the article, it's worth it). The int3 instruction is usually followed by random bytes that break the normal execution of the shellcode: Figure 14 Using int3 to raise the breakpoint exception. However, if we calculate the valued in the register EDI, we get the value 0x100. libb64-1.2.src.zip. olen = len * 4 / 3 + 4; /* 3-byte blocks to 4-byte */ *pos = '\0'; section for more details.). Following is the mapping table which is also called the Base64 index or alphabet table -. Is it possible? This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository. The latest version integrates new anti-analysis techniques, which results in it being significantly challenging to analyze. So to make string length multiple of 3 , we must add 2 bit padding to make length= 6. If the 5th byte of the decrypted URL-string is equal to s, GuLoader replaces the first 8 bytes with https://. This is Base64 encode/decode library for C++. Base64 encode your data without hassles or decode it into a human-readable format. 128 bits make 16 bytes (since 1 byte is 8 bits). the routine separately. To patch one instruction on which an exception is raised and replace it with a jump to a correct address in x32dbg, you can use the following script (you must replace 0x8B with a constant value from the sample you analyze): All the strings, including the URL for downloading the final payload, are encrypted and stored in a specific form in the shellcode: For the example above, we deobfuscated the code, clearing it of junk instructions and jumps. Author(s) | An example code is here. Why? Now, it will convert the ASCII to binary format 8-bit each. Work fast with our official CLI. * Returns: Allocated buffer of out_len bytes of encoded data, This is Base64 encode/decode library for C++. *pos++ = base64_table[(in[0] & 0x03) << 4]; *pos++ = '='; Programming | * Returns: Allocated buffer of out_len bytes of decoded data, It's not always necessary to have the highest level of encryption for every piece of data. if (tmp == 0x80) 2020-04-29: it turns out, this header file is not needed anymore. In each case, the database default collation is used. The JsonElement type provides array and object enumerators along with APIs to convert JSON text to common .NET types. . Then, one or two pad (=) characters are output depending on the following cases -. It's a textual encoding of binary data where the resultant text has nothing but letters, numbers and the symbols "+", "/" and "=". GuLoader uses the following combination of instructions to set TF in the EFALGS register: Figure 13 Setting a Trap Flag to raise the single-step exception. It's a convenient way to store/transmit binary data over media that is specifically used for textual data. characters that is both part of the subset common to most encodings, To further this system, when the ASCII character set was defined, only 00-7F were assigned characters. line_len += 4; An expression of type varbinary (n | max). if (out == NULL) /* However, it is still used in various parts of the GuLoader shellcode. New GuLoader samples receive zero detections on VirusTotal,ensuring its maliciouspayloads alsoremain undetected. What is the purpose of base 64 encoding and why it used in HTTP Basic Authentication? 97= 01100001, 98= 01100010, 99= 01100011, 100= 01100100, 011000, 010110, 001001, 100011, 011001, 00. so the last 6-bit is not complete so we insert two padding bit which equals four zeroes 0000. Base64 encode/decode. Firefox's bookmarks.html. Each of the 6-bit binary sequences from 0 to 63 are assigned a Base64 alphabet. To encode DOMStrings, you need to convert the UTF-16 DOMStrings to UTF-8 array of characters. This allows GuLoader samples to maintain a very low detection rate. I severely doubt any of them are in use today. But I think the adoption of 7-bit ASCII was primarily driven by punched paper tape formats, and its origins lie in telegraphy rather than inter-computer communication, @FelipeM slower, not faster. The VBScript variant stores the shellcode on a remote server. Checking if there are any VM-related drivers present, using the EnumDeviceDrivers API function. BASE64_ENCODE converts the value of a varbinary into a base64 encoded varchar. which it sets directly before exiting (lines 14 and 119). but, how? * base64_decode - Base64 decode and the executable is standalone, this is not a big problem: if (src[i] == '=') Second degree sensitive data is okay to be base64 encoded to make it unreadable by db administrators. What is the advantage of using Base64 encoding? else if (pad == 2) In the early days of computers, when telephone line inter-system communication was not particularly reliable, a quick & dirty method of verifying data integrity was used: "bit parity". Are you sure you want to create this branch? when you have Vim mapped to always print two? Convert string to ASCII binary format 8-bit. Learn more about the CLI. implemented using co-routines, which make the code more compact, easier to routine is entered, the switch moves control to the specific point directly return out; Base-64 encoding is a way of taking binary data and turning it into text so that it's more easily transmitted in things like e-mail and HTML form data. The Base64 encoding is described in the RFC 4648. If url_safe is true, the base64url string that is generated is incompatible with SQL Server's XML and JSON base64 decoders. For Example : In C and C++, this "null" character shows the end of a string. Optional integer literal or expression, which specifies whether the output of the encode operation should be URL-safe. A very popular way to encode binary data is Base64. Ways to find a safe route on flooded roads, Speed up strlen using SWAR in x86-64 assembly, Remove hot-spots from picture without touching edges. size_t olen; In this method, every byte transmitted would have 7-bits of data, and the 8th would be 1 or 0, to force the total number of 1 bits in the byte to be even. These 24-bit groups are then treated as 4 concatenated 6-bit groups. Finally a single pad (=) character is appended to the output. For example, when you send an email containing an image to your friend, your email software Base64 encodes the image and inserts the equivalent text into the message like so -. Therefore, when exiting the exception handler, control is transferred to the new address. Several years after its introduction, the threat posed by GuLoader continues to grow. with the function into an object in C++. As a result, we cannot determine the correct execution path without analyzing the code of the GuLoader VEH. The class implements RFC 4648 - https://tools.ietf.org/html/rfc4648. Therefore the bloating is only a mere 4/3 = 1.3333333 times the original. One example of such a system is Email (SMTP), which was traditionally designed to work with plain text data in the 7-bit US-ASCII character set. I've never seen a hash written as unsigned 8 bit integers, 0,1,255,36and displaying it with UTF-8 or any other encoding wouldn't make sense, how else would you display it other than with base64? Returned buffer is /** We got (T)01010100 (H)01001000 (S)01010011, Divide binary data into chunks of 6-bits. Therefore, in the new version, they replaced the URL scheme with random bytes. count = 0; At the very least you will learn how base64 encoding works. because 1 byte= 8bit = 256 possible characters? where each byte is represented by 2 bytes. in exactly this way, providing both a high-speed high-maintenance C interface, Any further resource regarding that would be greatly appreciated thank you. In reality, the code contains a large number of garbage and invalid instructions. Searching for QEMU related files: C:\Program Files\Qemu-ga\qemu-ga.exe and C:\Program Files\qga\qga.exe. size_t *out_len) http://www.chiark.greenend.org.uk/~sgtatham/coroutines.html. count the number of characters in a String. Therefore, per Base64 encoding, a 128-bit hash requires at least 128/6=22 characters, plus pad if any. . from a base64-encoded Base64 encoding and decoding is an important aspect of web development, as it allows you to convert binary data into ASCII text format and vice versa. out = os_malloc(olen); How do I base64 encode (decode) in C? Some transportation protocols only allow alphanumerical characters to be transmitted. Well, base64 encode strings when storing into the database and base64 decode when retrieving. For hashes, that is in fact far more common than base64. You never know -- some protocols may interpret your binary data as control characters (like a modem), or your binary data could be screwed up because the underlying protocol might think that you've entered a special character combination (like how FTP translates line endings). The combination of the next few instructions is intended to push the EFLAGS and set the TF (Trap Flag) bit to 1. Antivirus products are constantly evolving to become more sophisticated and better equipped to handle complex threats. It contains a lot of pseudo-random comments and some useless commands. The shellcode performed the main functions of loading the encrypted payload, decrypting it and launching it from memory. (To see how the libb64 codebase compares with some other BASE64 implementations On to the next section Download via the project page: */ Point to be noted : Length of the string should be in multiple of 3. In some cases download links to GuLoader malicious payloads stored in Google Drive remain active for very long periods of time. Here are examples of more URL-strings extracted from different samples: The payload decryption key is also stored in the same way as the encrypted strings but the key is not encrypted. line_len = 0; Programming The last chunk of input contains exactly 16 bits: Two zero bits are added to form three 6-bit groups. The payload decryption key is then XOR-ed with the calculated 2-bytes value: Figure 21 Calculating the final key used for decrypting the payload. C++ (Cpp) Curl_base64_encode - 30 examples found. can take it and do whatever you want with it. The numbers used and the mathematical operations that lead to the calculation of the zero value are always different. encodes binary data by treating it numerically and translating it into Example could be the following: you have a web service that accept only ASCII chars. You can rate examples to help us improve the quality of examples. Direct Base Classes: Base64EncoderIOS, std::ostream, All Base Classes: Base64EncoderIOS, std::ios, std::ostream. implementation is an example. This can be useful when you need to store binary data in a more readable format, such as when transmitting data over a network or when saving data in Continue reading Encode and Decode Base64 using JavaScript With Examples This year we also saw the use of a new trick: moving the encrypted shellcode to the cloud, and using a VBScript to download the shellcode. However, the resulting script is still heavily obfuscated. However, if the debugger is attached, the GuLoaders VEH is not called and execution follows the wrong path. The particular choice of base is due to the In the case of EXCEPTION_BREAKPOINT, the exception handler also looks for software breakpoints in the address space between the old EIP and the calculated new EIP values. is a library of ANSI C routines for fast encoding/decoding data into and SOLUTION You can use the following dataweave script to decode it successfully: This is to ensure that the data remains intact without modification during transport(Wiki, 2017). That code is compiled on following commands. Does that mean that all network type data passing should use some kind of encoding? count = 0; */ { * One hexadecimal digit is of one nibble (4 bits). The basis of this is an encoding table. * @len: Length of the data to be encoded without any licensing problems. GuLoader has been active for more than three years and is still undergoing further development. Is it possible to type a single quote/paren/etc. Even in a database, and. this project. using MS VCC++ Express 2010, using the base64.sln solution file in the The primary reason is to convert binary data to something passable. example # include < stdio.h > # include < string.h > # include < stdlib.h > # include " b64.h " int main (void) { unsigned char *str = " brian the monkey and bradley the kinkajou are friends "; . +,/. while (end - in >= 3) { # (padded with `=` to account for extra bits added), # The "URL and Filename safe" Base 64 Alphabet, RFC 4648: The Base16, Base32, and Base64 Data Encodings. It represents binary data in a printable ASCII string format by translating it into a radix-64 representation. At the time of uploading to VirusTotal (VT) on March 3, 2023, it had 0 detections: Figure 4 Zero detections of GuLoader sample in VT. Two days after it was uploaded, only 17 out of 59 vendors flagged this sample as malicious. *pos++ = (block[0] << 2) | (block[1] >> 4); @CholthiPaulTtiopic: I'm afraid I have no idea what you mean by "what about storage" but at this point I think we're somewhat off-topic. Using int3 as instruction as an anti-analysis technique was already implemented in the previous version of GuLoader. */ unsigned char * base64_encode (const unsigned char *src, size_t len, size_t *out_len) { unsigned char *out, *pos; const unsigned char *end, *in; size_t olen; int line_len; olen = len * 4 / 3 + 4; /* 3-byte blocks to 4-byte */ olen += olen / 72; /* line feeds */ olen++; /* nul ter. AI/ML Tool examples part 3 - Title-Drafting Assistant. For example, an RLE decompressing routine, adapted from the article: As can be seen from this example, a coroutine depends on a state variable, Some implementations are released under The steps followed by the base64 algorithm are as follow: I use it in a practical sense when we transfer large binary objects (images) via web services. * nul terminated to make it easier to use as a C string. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Base64 is a binary-to-text encoding scheme. Using base64, we can produce the encoded output of our desired length (6, 8, or 10). The resulting value is then added to the EIP value in the exception context. The chunks of 6-bit binary data will now be converted to decimal We see evidence that GuLoader is currently being used to distribute the following malware: Early GuLoader samples managed to avoid detection by antivirus products, but later different security solutions became capable of detecting this malware. Static analysis of NSIS script and encrypted shellcode is also possible. It's used in various places: from encoding bytes for sending over the internet, to storing public/private keys in text format. The C code uses a little trick which We see that this new script contains the function Gothites9, which implements cutting the passed string starting from the second character with a step of 3. libb64 if (olen < len) Is there any class to do that operation (I want an API). The problem with binary data is that it contains null characters which in some languages like C,C++ represent end of character string so sending binary data in raw form containing NULL bytes will stop a file from being fully read and lead in a corrupt data. The default value is 0. This mapping between the 6-bit binary sequence and the corresponding Base64 alphabet is used during the encoding process. I did this because I needed a fast C++ implementation of base64 Base64 encoding works with a 65-character subset of the US-ASCII charset. What is the real purpose of Base64 encoding? However, if a debugger is attached, the control is transferred to the debuggers interrupt handler which typically pauses the programs execution. if (dtable[src[i]] != 0x80) ), @yokees: There is no guarantee, they're just characters that are. Although, It was later extended to support non US-ASCII text messages as well as non-text messages such as audio and images, It is still recommended to encode the data to ASCII charset for backward compatibility. * or %NULL on failure */ BFSI uses cookies on this site. A very thorough and enlightening essay on co-routines in C, using Since an encryption key does not have to be text but raw bytes it is sometimes necessary to store it in a file or database, which Base64 comes in handy for. olen = count / 4 * 3; The nul terminator is There are multiple implementations of base64 with slight differences. Base64 transforms any input into an encoding that only uses alphanumeric characters, +, / and the = as a padding character. Base64 is one of these types of encodings. (in[1] >> 4)]; You've got the size of SHA and MD5 reversed; SHA is usually (but not always) 256, and MD5 is 128. Contribute to jwerle/b64.c development by creating an account on GitHub. times when the line breaks are known . Source Forge for hosting However, the btoa() function doesn't recognize DOMStrings which are 16-bit encoded. Javascript has a built-in function named btoa() that you can use to perform Base64 encoding. This allows for a fast, multi-thread-able implementation, which is safe to use If you want to send a message with attachments, but the protocol (for example . I need to convert them to PEM base64 in c. I looked in openssl library but i could not find any function. pos -= 2; Access via CVS is also possible. So if you don't like hacks, please do not go on. http://www.chiark.greenend.org.uk/~sgtatham/coroutines.html Building and Installing | a base 64 representation. executable file in the base64 directory. Encode unsigned char * source with size_t size. . As you can see we cant put char / in URL if we want to send last visited URL as parameter because we would break attribute/value rule for MOD rewrite GET parameter. and maintain. if (pad == 1) sign in You'd display the hash as hex, not decimal. There are many uses of base64 beyond transmitting. Why is it "Gaudeamus igitur, *iuvenes dum* sumus!" There are several issues with the example here, and I've unfortunately seen people copying this into their productions systems before. Yannic Bonenberger also notified me of a concurrency issue if the library was used in a multi-threaded environment. @Backwards_Dave Each 6 bits are expressed in 8 bits. c++; class; encoding; base64; binary-data; Share. This work is released into the Public Domain. The shellcode started using three different patterns to throw exceptions and break the normal flow of code execution. } Another Example:: uenc = url encoded = aHR0cDovL2xvYy5tYWdlbnRvLmNvbS9hc2ljcy1tZW4tcy1nZWwta2F5YW5vLXhpaS5odG1s = http://loc.querytip.com/asics-men-s-gel-kayano-xii.html. eg in javascript atob function Is there meaning the server to encode a json file to base64 format? Padding bit is represented by = sign. traditionally not 8-bit clean. Difference between encoding and encryption. for details. Why is the logarithm of an integer analogous to the degree of a polynomial? * base64_encode - Base64 encode which can be found on-line here: The available code is mostly slow as well, and complicated to understand, use When base64 encoding is used in email encryption it is called Privacy enhanced Electronic mail (PEM). In C and C++, this "null" character shows the end of a string. break; int line_len; Why use the binary number 64 in base64 as opposed to whole ASCII set? Why 64? const unsigned char *end, *in; number format. os_free(out); Base64 uses a subset of displayable ASCII characters, and is therefore a useful encoding for storing The advanced defense evasion ofGuLoadermade it a favored tool among threat actors for delivering malware. Few of the routers survived into the 90s. It contains junk instructions, and important values are calculated dynamically using XOR operations: However, after the decompilation in IDA this code looks very simple: As you can see, VEH actions are slightly different depending on the exception code. Now, it is equal. We got VEhT. But there's probably no practicality in using Base256. unsigned char dtable[256], *out, *pos, block[4], tmp; Do I understand correctly, that 64 is the best choice as it is the highest power of two that is convertible to a printable ASCII character (there is 95 of them)? Counting the number of Windows, using the EnumWindows API function (. The Base64 method of encoding is used when binary data, such as images or video, is transmitted over systems that are designed to transmit data in a plain-text (ASCII) format. Base 64 maps all the binary characters into several standard ascii letters and numbers and punctuation so they won't be mangled this way. and also on-line at The "standard" alphabet uses A-Z, a-z, 0-9 and + and /, with = as a padding character. It basically boils down to this: I put this work in the public domain, and you The extra 65th character (=) is used for padding. If nothing happens, download GitHub Desktop and try again. Note that although Base64 is often used in cryptography is not a security mechanism. So then, under which license do I release this code? It is interesting that all lines in the nested script are stored in encoded form, except for the line with the URL. An example of data being processed may be a unique identifier stored in a cookie. Implementation Details | After converting to binary format, it will divide binary data into *pos++ = (block[2] << 6) | block[3]; Base64 is for that. How do you apply patch file downloaded from gerrit? How do I Derive a Mathematical Formula to calculate the number of eggs stacked on a crate? } Starting from the end of 2022, the GuLoader shellcode uses a new anti-analysis technique, which consists of breaking the normal flow of code execution by deliberately throwing a large number of exceptions and handling them in a vector exception handler that transfers control to a dynamically calculated address. Earlier we can not transfer a large amount of data like files because it is made up of 2 bit bytes but our actual network uses 2 bit bytes. So what I did to support full 4-byte unicode over MySQL's utf8? and read the So, to tackle this problem BASE64 came along. Gratcias! Mostly, I've seen it used to encode binary data in contexts that can only handle ascii - or a simple - character sets. If we look at the contents of the pa0 variable after adding the omissions and hyphens, we get the following script: Figure 6 GuLoader obfuscated PowerShell script. Library: Foundation The input is divided into groups of three bytes (24 bits) each. Please It is DAMN fast, if I may say so myself. The use of encryption and storing payloads in a raw binary format without any headers and separate from the loader makes them totally invisible to antiviruses. for details. because some media are made for streaming text. For example: "abcd3RkPUYY_Ybvckj==", in this case, it is an underscore character. size_t i, count, olen; encoding and decoding, chunks of 6-bits each. 26 Uppercase alphabets: i.e., A,B,C,D,,Z, 26 Lowercase alphabets: i.e., a,b,c,d,,z, 2 special characters (these characters depends on operating system): i.e. It is designed to carry data stored in binary format across the network channels. http://sourceforge.net/cvs/?group_id=152942. Copyright 2022, Applied Informatics Software Engineering GmbH and Contributors, Applied Informatics Software Engineering GmbH and Contributors. base64_encode () comes in two overloaded versions: std::string base64_encode (std::string const& s, bool url = false); std::string base64_encode (unsigned char const*, unsigned int len, bool url = false); Both of these functions encode data as Base 64 and return the encoded string as a std::string. static const unsigned char base64_table[65] = * or %NULL on failure Step 2: Convert the 6-bit sequences to Base64 alphabets by indexing into the Base64 index table. This eventually causes the application to crash. What is Base94 encoding and how does it work? At first glance, it is unclear what happens in this piece of code. Encoding from standard input to standard output is as simple as. Base64Encoder(std::ostream & ostr,int options = 0); POCO C++ Libraries 1.12.2-all copy of which can be found in the LICENSE file in the distribution, either the GNU/GPL, or a BSD-variant, which is not what I require. Base64 Encode. Command-line Use, Change into the The term Base64 originates from a specific MIME content transfer encoding. Convert chunks of 6-bit binary data to decimal numbers. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Meet Base64 Decode and Encode, a simple online tool that does exactly what it says: decodes from Base64 encoding as well as encodes into it quickly and easily. lets prove it. Are you sure you want to create this branch? What is this object inside my bathtub drain that is causing a blockage? But why Base-64? Java 8 introduced a new class called Base64 which contains convenience functions to Base64 encode a sequence of bytes and also decode a Base64 encoded string. I went into trouble when I discovered that MySQL's utf8 does not support 4-byte unicode characters since it uses a 3-byte version of utf8. Acknowledgement. Pad with zero bits at the end to form an integral no of 6-bit groups. line_len += 4; In the case of exception 0x80000003 (EXCEPTION_BREAKPOINT), the byte at offset 1 is taken and also XORs with the constant. minimize the delay when transferring receipt characters for signing. This causes the access violation exception (0xC0000005). To help understand the obfuscation complexity, this is part of the original code corresponding to the previous example: Figure 18 Composing encrypted strings in the heavily obfuscated GuLoader shellcode. * @out_len: Pointer to output length variable We use cookies to enable faster and easier experience for you. * What should be the criteria of convergence over ENCUT? dtable[base64_table[i]] = (unsigned char) i; Base64 is a group of similar binary-to-text encoding schemes that represent binary data in an ASCII string format by translating it into a radix -64 representation. We got 010101 000100 100001 010011, Convert chunks of 6-bit binary data to decimal numbers.We got 21 4 33 19, Convert decimals to string according to the base64 Index Table. This allows content creators or web developers to embed images or files inline in documents. The exception is handled in GuLoader by the registered VEH which calculates the new address to continue the shellcode execution. This script is called either by using the IEX command (if the OS is 32-bit) or passed as a parameter to the PowerShell interpreter called from the SysWOW64 folder (if the OS is 64-bit). Simply copy the executable somewhere in your path. (and others such as MinGW and Cygwin), or using a Visual Studio solution. Check Point Threat Emulation provides protection against this threat: 1994-document.write(new Date().getFullYear()) Check Point Software Technologies LTD. All rights reserved. Note: The characters are directly written to the ostream's streambuf, thus bypassing the ostream. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. We are graduating the updated button styling for vote arrows. Currently, the most common versions are based on the VBScript and the NSIS installer. Key takeaways. Header: Poco/Base64Encoder.h. For more information on this technique, see "Coroutines in C", by Simon Tatham, When the CPU encounters the int3 instruction in the absence of a debugger, it generates a breakpoint exception (0x80000003) and the registered VEH is called. A tag already exists with the provided branch name. https://evasions.checkpoint.com/techniques/cpu.html#check-if-being-run-in-Hypervisor-via-cpuid, https://evasions.checkpoint.com/techniques/timing.html#rdtsc, https://evasions.checkpoint.com/techniques/ui-artifacts.html#check-number-of-top-level-windows, https://anti-debug.checkpoint.com/techniques/process-memory.html#patch_ntdll_dbgbreakpoint, https://anti-debug.checkpoint.com/techniques/process-memory.html#patch_ntdll_dbguiremotebreakin, https://anti-debug.checkpoint.com/techniques/interactive.html#ntsetinformationthread, Malware Analysis: GuLoader Dissection Reveals New Anti-Analysis Techniques and Code Injection Redundancy, managed to decrypt URLs in the previous versions of the shellcode, OPWNAI : Cybercriminals Starting to Use ChatGPT, OpwnAI: AI That Can Save the Day or HACK it Away, BlindEagle Targeting Ecuador With Sharpened Tools, hxxps://drive.google.com/uc?export=download&id=1BZ2BJVzqOMDwarpjiTzKEiwa42W1Dj9q, hxxps://drive.google.com/uc?export=download&id=1soTWv6y3rkBBbmMcBMOwovCqXxU4UQRB, KlshsShadrive.google.com/uc?export=download&id=1OSjh65P9X1Tx4cIemJXvrIa3Lt7pUc5C, AppesNondrive.google.com/uc?export=download&id=1BMRiKvpSFYvKsNn6ilsl9DD3vFcz338C, ReseSyn45.88.66.147/kZDkFdCKTkJdSpwPQkKt70.bin, https://drive.google.com/uc?export=download&id=1BZ2BJVzqOMDwarpjiTzKEiwa42W1Dj9q, https://drive.google.com/uc?export=download&id=1soTWv6y3rkBBbmMcBMOwovCqXxU4UQRB, http://34.138.169.8/wp-content/themes/seotheme/CbwPtnKqeAYGeixiNB73.inf. So `` HELLO '' is stored like this: now lets dive into how base64 works... Downloader that has been used in http Basic Authentication in documents some protocols which fail... Two nibbles make 8 bits which are also called the base64 is used... Script. ; abcd3RkPUYY_Ybvckj== & quot ; NULL & quot ; character shows the end of a string base64! First glance, it 's not multiple of 3, c base64 encode example will get the wifi of... Encoding that only uses alphanumeric characters, +, / and the corresponding base64 alphabet restore... Padding character and change into the database default collation is used to binary. Bits at the end of a concurrency issue if the library was used in http Basic Authentication this article you! Am thankful for the price of safety interest without asking for consent came. B, C, D,.Z not find any function, that is in fact more! Before transmitting commonly used when there is a reasonably good source of more information,... Get around this, people encode the binary characters into several standard ASCII letters and numbers and so... Base64 decode when retrieving originates from a specific MIME content transfer encoding standalone! Bytes with https: // cookies to enable faster and easier experience c base64 encode example you only allow characters. ) in C and C++, this is base64 encode/decode library for C++ deobfuscating! Logarithm of an integer analogous to the debuggers interrupt handler which typically pauses programs... An anti-analysis technique was already implemented in the article, it 's not multiple of 3, we add! Requires at least 128/6=22 characters, plus pad if any variant, samples based on the VBScript variant stores shellcode! Doubt any of them are in use today the above encoded textual data to be transmitted bits: four bits. Bytes of encoded data, this header file is not a security mechanism do I Derive mathematical... Gmbh and Contributors, Applied Informatics software Engineering GmbH and Contributors it `` igitur... 128-Bit output which is represented using a syntax similar to e.g web.... Python has a built-in function named btoa ( ) function does n't any. > > 2 ] ; code for standalone encoding and how does it?! Result for the line with the URL scheme with random bytes > 2 ] code! Are also called the base64 encoding schemes are commonly used when there a. Of eggs stacked on a remote server debugger calling the NtSetInformationThread function with the ThreadHideFromDebugger ( resource... Improve the quality of examples if we calculate the valued in the nested script stored! Mean that all lines in the previous GuLoader versions JSON base64 decoders looks. Alphabets i.e., a, B, C, D,.Z evolving to become more sophisticated and equipped... Fact far more common than base64 to our use of cookies specifically used textual. The Access violation exception ( 0xC0000005 ) why is it `` Gaudeamus igitur, * iuvenes dum *!. As background-image decoding, chunks of 6-bits each an account on GitHub anti-analysis techniques, which specifies the... This `` NULL '' character shows the end to form two 6-bit.. = os_malloc ( olen ) ; use Git or checkout with SVN using the URL... Buffer 's state on VirusTotal, ensuring its maliciouspayloads alsoremain undetected debug registers: Figure 9 GuLoader... Than base64 in you 'd display the hash as hex, not decimal do we need to binary... On GitHub: Figure 21 Calculating the final key used for textual to... Jump address is calculated, lets look at the end to form two 6-bit groups new line.... Of data being processed may be a c base64 encode example identifier stored in encoded form, except for line... Pos = out = os_malloc ( olen ) ; how do I Derive a Formula... Contributors, Applied Informatics software Engineering GmbH and Contributors Figure 21 Calculating the final used... Base Classes: Base64EncoderIOS, std::ostream in Kali Linux len: length of the operation. Handled in GuLoader by the registered VEH which calculates the new address them are in use today ;. Files: C: \Program Files\Qemu-ga\qemu-ga.exe and C: \Program Files\qga\qga.exe bits: four zero bits are expressed 8! Characters are output depending on external files discussion and an interesting history lesson, thanks a... Providing both a high-speed high-maintenance C interface, any further resource regarding that would be greatly appreciated thank you QEMU... Pad character if zero bits at the VEH code is obfuscated decoding, chunks of 6-bits and it. C, D,.Z = as a part of c base64 encode example legitimate business interest without asking for consent slight! 1.3333333 times the original, thus bypassing the ostream for textual data n't like hacks please. Anti-Debugging techniques hassles or decode it back to a remote server = base64_table [ in 0! To jwerle/b64.c development by creating an account on GitHub Windows, using RDTSC in combination CPUID. The 6-bit binary sequences from 0 to 63 are assigned a base64 alphabet is used to encode DOMStrings, need! Unicode over MySQL 's utf8 into your RSS reader could n't pass the. And code Injection Redundancy feed character ( U+000A ) replaces the first 8 bytes with https:.! Cpp ) Curl_base64_encode - 30 examples found calculation of the debug registers: 21. When you have Vim mapped to always print two under CC BY-SA uenc = URL encoded = aHR0cDovL2xvYy5tYWdlbnRvLmNvbS9hc2ljcy1tZW4tcy1nZWwta2F5YW5vLXhpaS5odG1s =:... Call close ( ) when done writing data, especially base64.sln solution in... Essentially each 6 bits of data > > 2 ] ; code for encoding. This code did this because I needed a fast C++ implementation of base64 base64 encoding works I am thankful the... Represented using a Visual Studio solution anti-analysis techniques, which specifies whether the output is URL-safe. the previous of. Is base64 c base64 encode example library for C++ the JsonElement type provides array and object enumerators along APIs! The end of a string '' ; the nul terminator is there meaning the to... The same way the next few instructions is intended to push the EFLAGS and set TF. But I could not find any function glance, it is designed to resist.! ) Curl_base64_encode - 30 examples found printable ASCII string format they are all binary! Example of data Git commands accept both tag and branch names, so creating this may! Convert chunks of 6-bit groups with the URL scheme with random bytes security mechanism practicality in using.. Came along TF ( Trap Flag ) bit to 1 lets consider a with! Control is transferred to the previous version of GuLoader is aprominent shellcode-based downloader has. See how the jump address is calculated, lets look at the end of the input divided! Not been listed are creating this branch input into an encoding that only uses alphanumeric characters +. Of pseudo-random comments and some useless commands to embed raw image data into human-readable. That is specifically used for decrypting the payload decryption key eggs stacked on a remote server uenc URL. Processed may be a unique identifier stored in Google Drive ) someone knows algorithm itself has not changed in to. / { * One hexadecimal digit is of One nibble ( 4 bits ) each 1... And why it used in http Basic Authentication deliver a wide range ofthe most wantedmalware services are designed... Patterns to throw exceptions and break the normal flow of code execution. debuggers interrupt which! Encode your data without hassles or decode it back to a string in Node.js * in ; number.! Also notified me of a string to be noted: One padding bit four. The ASCII to binary format across the network channels within scripts, to avoid depending on the example. Line feed character ( U+000A ) it sets directly before exiting ( 14... Originates from a specific MIME content transfer encoding in VEH turn are 32 * 4=128 bits characters. It represents binary data is base64 encode/decode library for C++ decoding executables than `` Gaudeamus igitur *. We must add 2 bit padding to make length= 6 embed images or inline! Guloader VEH base64.sln solution file in the exception handler, control is transferred the... B, C, D,.Z well, base64 encode images before?. Some cases download links to GuLoader malicious payloads stored in binary format divide... To code encryption, GuLoader utilizes many other c base64 encode example including anti-debugging and evasion. Few instructions is intended to push the EFLAGS and set the TF ( Trap Flag ) to! The final key used for textual data all lines in the GuLoader shellcode are always different ; various of... '= ' ; after converting to binary format across the network channels JsonElement type provides array and object along... Of time source of more information them to PEM base64 in c. looked! Encoded without any licensing problems 8 bits so if you do n't hacks. Support full 4-byte unicode over MySQL 's utf8 bit is enabled, the... Class implements RFC 4648 - https: // are 64 total characters that go into the.... Incompatible with SQL server 's XML and JSON base64 decoders proper completion of the 6-bit binary sequence the. Performed the main functions of loading the encrypted payload is uploaded to a remote server also improving... Chunk of input contains exactly 8 bits is used to embed raw image data into chunks of each. Logo 2023 Stack Exchange Inc ; user contributions licensed under CC BY-SA no of 6-bit groups value.
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