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.Dd October 14, 2015 .Dt SHAKE 3 .Os .Sh NAME .Nm SHAKE .Nd NIST FIPS PUB 202: SHA-3 Standard: Permutation-Based Hash and Extendable-Output Functions .Sh SYNOPSIS n sha3.h .Ft void .Fn SHAKE128_Init "SHAKE128_CTX *ctx" .Ft void .Fn SHAKE128_Update "SHAKE128_CTX *ctx" "const uint8_t *buf" "size_t len" .Ft void .Fn SHAKE128_Final "uint8_t *output[]" "size_t outlen" "SHAKE128_CTX *ctx" .Ft void .Fn SHAKE256_Init "SHAKE256_CTX *ctx" .Ft void .Fn SHAKE256_Update "SHAKE256_CTX *ctx" "const uint8_t *buf" "size_t len" .Ft void .Fn SHAKE256_Final "uint8_t *output[]" "size_t outlen" "SHAKE256_CTX *ctx" .Sh DESCRIPTION The .Nm functions implement the extendable-output functions of the NIST SHA-3 standard, FIPS PUB 202. The .Nm functions absorb an arbitrary-length message m and yield an arbitrary-length output SHAKE128(m) or SHAKE256(m), truncated to a specified number of octets.
p Before using the .Nm functions, applications should first call .Xr SHA3_Selftest 3 and confirm that it succeeded.
p Only the .Nm SHAKE128 functions are specified in detail; the .Nm SHAKE256 functions are analogous.
p The caller must allocate memory for a .Vt SHAKE128_CTX object to hold the state of a SHAKE128 computation over a message. .Vt SHAKE128_CTX objects may be copied or relocated in memory. l -tag -width abcd t Fn SHAKE128_Init "ctx" Initialize a SHAKE128 context. Must be done before any other operations on .Fa ctx . t Fn SHAKE128_Update "ctx" "data" "len" Append .Fa len octets at .Fa data to the message. t Fn SHAKE128_Final "output" "outlen" "ctx" Store at .Fa output the first .Fa outlen octets of the SHAKE128 output for the message obtained by concatenating all prior inputs to .Fn SHAKE128_Update on .Fa ctx .
p Subsequent use of .Fa ctx is not allowed, unless it is reinitialized with .Fn SHAKE128_Init . .El .Sh SEE ALSO .Xr keccak 3 , .Xr sha3 3 , .Xr SHA3_Selftest 3 .Sh STANDARDS .Rs .%A National Institute of Standards and Technology .%T SHA-3 Standard: Permutation-Based Hash and Extendable-Output Functions .%O FIPS PUB 202 .%D August 2015 .Re .Sh AUTHORS .An Taylor R Campbell Aq campbell+sha3@mumble.net