The advantage is that this table of values, instead of being of 16 symbols (hexadecimal) is of 64, allowing to contain much more information for each character transmitted, saving a lot of bandwidth in communications very limited in speed. Base64 defines a table that allows to transform between a binary value and a map defined for this encoding. If an embedded device is found without a command line utility for base64, it is common to be able to encode from Python, Perl or other languages on the device. Although it is less common to find a utility to generate the base64 of a file, many modern languages include libraries to do so. For more information about the format see the following link.Ġ0000000 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46 |0123456789ABCDEF|Ġ0000010 0a 2f 2a 20 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a |./* ************|Īs with hexdump, base64 is a useful format for transmitting an encoded binary over a channel that only supports printable characters. To restore this format to a raw binary one of the most common tools is xxd with the ‘ – r’ parameter of revert. Normally a hexdump with these tools consists of an address column, a column with the memory contents in hexadecimal and finally an optional column with the contents encoded in text. One of the most common options in this case for memory dump is hexdump or one of its alternatives. S11F001C4BFFFFE5398000007D83637880010014382100107C0803A64E800020E9Īs discussed in the article OWASP FSTM, stage 2: Obtaining IOT device firmware, sometimes you will have access to devices through text interfaces and with limited tools. To convert this format to binary, the same tools can be used as in the previous section. More information can be found at this link. It can be distinguished because in this case the start code is an ‘S’. Again, a start code is defined along with different fields to describe data records in hexadecimal format. To obtain a binary from such a file, multiple tools can be used such as Intel_Hex2Bin, or SRecord. ![]() More details on the format can be found at the following link. ![]() Although the format is more complex, for simple cases it can be summarized in that for each line it usually includes the start code, a record length, the record address, a record type (data, usually) and a final checksum. Intel HEXīeing one of the oldest formats for representing the contents of memories, it can be characterized by its line start code, the colon ‘:’. The following is a summary of the most common formats for this type of task and their typical characteristics. However, a text editor and hexadecimal editor should be sufficient to verify the information of the tools used or to find out in which format a dump can be found. The researcher must consult the documentation of the tool used to be sure to perform a conversion to binary format. In this first step, it relies on previous information to know in which format the firmware dump has been performed. Many of the analysis tools available, will be based on binary formats and obtaining a binary is an important task in case at some point you want to perform a full emulation of the device. The goal of this section is to convert that format into a raw binary format. Obtaining a raw binary dumpĭepending on the techniques used in step two ( OWASP FSTM, stage 2: Obtaining IOT device firmware) of this guide, the firmware dump may be in different formats. Finally, metrics, tools and techniques that allow us to identify sections, formats and signatures within a firmware for later extraction are listed. A section is also dedicated to those cases in which our firmware may include more data than desired, which may alter the results of subsequent tests. Next, it is proposed to transform the available firmware dump format into a standardized binary format for further analysis. ![]() With this context in mind, it will be possible to make a judicious choice between the various tools and techniques here proposed for analyzing firmware. For this reason, it is important not to lose the context in which the analysis is performed and to consider all the information gathered in the previous steps. ![]() It is common during firmware analysis to be confronted with undocumented formats, proprietary solutions, and even encrypted data. Different techniques that can help extracting data from these dumps will be reviewed down below. Manual analysis with a hexadecimal editorĪnalyzing a firmware dump is not a simple task that can be summarized in simple steps to obtain a formula valid for all cases.
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