Those 8 octal digits can be split into pairs ( 23 26 05 56), and each pair is converted to decimal to yield 19 22 05 46. For example, the hexadecimal representation of the 24 bits above is 4D616E. Such conversion is available for both advanced calculators and programming languages. Hexadecimal to octal transformation is useful to convert between binary and Base64. = padding characters might be added to make the last encoded block contain four Base64 characters. Groups of 6 bits (6 bits have a maximum of 2 6 = 64 different binary values) are converted into individual numbers from start to end (in this case, there are four numbers in a 24-bit string), which are then converted into their corresponding Base64 character values.Īs this example illustrates, Base64 encoding converts three octets into four encoded characters.Įncoding of source characters M, a, n in Base64. These three values are joined together into a 24-bit string, producing 010011010110000101101110. Encoded in ASCII, the characters M, a, and n are stored as the byte values 77, 97, and 110, which are the 8-bit binary values 01001101, 01100001, and 01101110. In the above quote, the encoded value of Man is TWFu. Here is a well-known idiom from distributed computing: The more typical use is to encode binary data (such as an image) the resulting Base64 data will only contain 64 different ASCII characters, all of which can reliably be transferred across systems that may corrupt the raw source bytes. The example below uses ASCII text for simplicity, but this is not a typical use case, as it can already be safely transferred across all systems that can handle Base64. This is the Base64 alphabet defined in RFC 4648 §4. For instance, uuencode uses uppercase letters, digits, and many punctuation characters, but no lowercase. The earliest instances of this type of encoding were created for dial-up communication between systems running the same OS, for example, uuencode for UNIX and BinHex for the TRS-80 (later adapted for the Macintosh), and could therefore make more assumptions about what characters were safe to use. Other variations share this property but differ in the symbols chosen for the last two values an example is UTF-7. For example, MIME's Base64 implementation uses A– Z, a– z, and 0– 9 for the first 62 values. This combination leaves the data unlikely to be modified in transit through information systems, such as email, that were traditionally not 8-bit clean. The general strategy is to choose 64 characters that are common to most encodings and that are also printable. Upon execution a file named T1140_calc_decoded.The particular set of 64 characters chosen to represent the 64-digit values for the base varies between implementations. (Citation: Volexity PowerDuke November 2016) Atomic Tests Atomic Test #1 - Deobfuscate/Decode Files Or Information The user may also be required to input a password to open a password protected compressed/encrypted file that was provided by the adversary. Sometimes a user's action may be required to open it for deobfuscation or decryption as part of User Execution. One such example is the use of certutil to decode a remote access tool portable executable file that has been hidden inside a certificate file.(Citation: Malwarebytes Targeted Attack against Saudi Arabia) Another example is using the Windows copy /b command to reassemble binary fragments into a malicious payload.(Citation: Carbon Black Obfuscation Sept 2016) Methods for doing that include built-in functionality of malware or by using utilities present on the system. They may require separate mechanisms to decode or deobfuscate that information depending on how they intend to use it. Try it using Invoke-Atomic Deobfuscate/Decode Files or Information Description from ATT&CKĪdversaries may use Obfuscated Files or Information to hide artifacts of an intrusion from analysis. Atomic Test #8 - XOR decoding and command execution using Python.Atomic Test #7 - Linux Base64 Encoded Shebang in CLI.Atomic Test #6 - Hex decoding with shell utilities.Atomic Test #5 - Base64 decoding with shell utilities.Atomic Test #4 - Base64 decoding with Perl.Atomic Test #3 - Base64 decoding with Python.Atomic Test #2 - Certutil Rename and Decode.Atomic Test #1 - Deobfuscate/Decode Files Or Information.Deobfuscate/Decode Files or Information.
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