27 lines
1.1 KiB
Markdown
27 lines
1.1 KiB
Markdown
<h1 align="center">PKCS7-Padding</h1>
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Implementation of PKCS7 padding in C. It can be used to pre-prepare data before block cipher using (for example, AES).
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# Algorithm description
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PKCS7 is described in [RFC 5652](https://tools.ietf.org/html/rfc5652#section-6.3).
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Some content-encryption algorithms assume the input length is a
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multiple of k octets, where k is greater than one. For such
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algorithms, the input shall be padded at the trailing end with
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k-(lth mod k) octets all having value k-(lth mod k), where lth is
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the length of the input. In other words, the input is padded at
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the trailing end with one of the following strings:
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01 -- if lth mod k = k-1
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02 02 -- if lth mod k = k-2
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.
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.
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.
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k k ... k k -- if lth mod k = 0
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The padding can be removed unambiguously since all input is padded,
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including input values that are already a multiple of the block size,
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and no padding string is a suffix of another. This padding method is
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well defined if and only if k is less than 256.
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