94 lines
1.9 KiB
Text
94 lines
1.9 KiB
Text
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.TH CHACHA 2
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.SH NAME
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setupChachastate, chacha_setblock, chacha_encrypt, chacha_encrypt2 - chacha encryption
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.SH SYNOPSIS
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.B #include <u.h>
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.br
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.B #include <libc.h>
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.br
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.B #include <mp.h>
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.br
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.B #include <libsec.h>
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.PP
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.B
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void setupChachastate(Chachastate *s, uchar key[], ulong keylen, uchar *nonce, int rounds)
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.PP
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.B
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void chacha_encrypt(uchar *data, ulong len, Chachastate *s)
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.PP
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.B
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void chacha_encrypt2(uchar *src, uchar *dst, ulong len, Chachastate *s)
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.PP
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.B
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void chacha_setblock(Chachastate *s, u32int blockno)
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.SH DESCRIPTION
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.PP
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Chacha is D J Berstein's symmetric stream cipher, as modified by RFC7539. It supports
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keys of 256 bits (128 bits is supported here for special purposes). It has an underlying block size of 64 bytes
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(named as constant
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.BR ChachaBsize ).
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.PP
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.I SetupChachastate
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takes a reference to a
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.B Chachastate
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structure, a
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.I key
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of
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.I keylen
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bytes, which should normally be
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.BR ChachaKeylen ,
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a
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.I nonce
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or initialisation vector of
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.B ChachaIVlen
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bytes (set to all zeros if the argument is nil),
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and the number of
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.I rounds
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(set to the default of 20 if the argument is zero).
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With a keylength of 256 bits (32 bytes) and 20
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.IR rounds ,
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the function implements the Chacha20 encryption function of RFC7539.
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.PP
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.I Chacha_encrypt
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encrypts
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.I len
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bytes of
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.I buf
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in place using the
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.B Chachastate
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in
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.IR s .
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.I Len
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can be any byte length.
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Encryption and decryption are the same operation given the same starting state
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.IR s .
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.PP
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.I Chacha_encrypt2
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is similar, but encrypts
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.I len
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bytes of
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.I src
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into
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.I dst
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without modifying
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.IR src .
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.PP
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.I Chacha_setblock
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sets the Chacha block counter for the next encryption to
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.IR blockno ,
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allowing seeking in an encrypted stream.
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.SH SOURCE
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.B /sys/src/libsec
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.SH SEE ALSO
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.IR mp (2),
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.IR aes (2),
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.IR blowfish (2),
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.IR des (2),
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.IR dsa (2),
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.IR elgamal (2),
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.IR rc4 (2),
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.IR rsa (2),
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.IR sechash (2),
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.IR prime (2),
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.IR rand (2)
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