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/*
* SipHash Implementation
*
* For highlevel documentation of the API see the header file and the docbook
* comments. This implementation is based on the reference implementation of
* SipHash, written by Jean-Philippe Aumasson and Daniel J. Bernstein, and
* released to the Public Domain.
*
* So far, only SipHash24 is implemented, since there was no need for other
* parameters. However, adjusted c_siphash_append_X() and
* C_siphash_finalize_Y() can be easily provided, if required.
*/
#include <stddef.h>
#include <stdint.h>
#include "c-siphash.h"
#define _public_ __attribute__((__visibility__("default")))
static inline uint64_t c_siphash_read_le64(const uint8_t bytes[8]) {
return ((uint64_t) bytes[0]) |
(((uint64_t) bytes[1]) << 8) |
(((uint64_t) bytes[2]) << 16) |
(((uint64_t) bytes[3]) << 24) |
(((uint64_t) bytes[4]) << 32) |
(((uint64_t) bytes[5]) << 40) |
(((uint64_t) bytes[6]) << 48) |
(((uint64_t) bytes[7]) << 56);
}
static inline uint64_t c_siphash_rotate_left(uint64_t x, uint8_t b) {
return (x << b) | (x >> (64 - b));
}
static inline void c_siphash_sipround(CSipHash *state) {
state->v0 += state->v1;
state->v1 = c_siphash_rotate_left(state->v1, 13);
state->v1 ^= state->v0;
state->v0 = c_siphash_rotate_left(state->v0, 32);
state->v2 += state->v3;
state->v3 = c_siphash_rotate_left(state->v3, 16);
state->v3 ^= state->v2;
state->v0 += state->v3;
state->v3 = c_siphash_rotate_left(state->v3, 21);
state->v3 ^= state->v0;
state->v2 += state->v1;
state->v1 = c_siphash_rotate_left(state->v1, 17);
state->v1 ^= state->v2;
state->v2 = c_siphash_rotate_left(state->v2, 32);
}
/**
* c_siphash_init() - initialize siphash context
* @state: context object
* @seed: 128bit seed
*
* This initializes the siphash state context. Once initialized, it can be used
* to hash arbitrary input. To feed data into it, use c_siphash_append(). To get
* the final hash, use c_siphash_finalize().
*
* Note that the siphash context does not allocate state. There is no need to
* deserialize it before releasing its backing memory.
*
* The hashes generated by this context change depending on the seed. Every
* user is highly inclined to provide their unique seed. If no stable hashes
* are needed, a random seed will do fine.
*
* Right now, only SipHash24 is supported. Other SipHash parameters can be
* easily added if required.
*/
_public_ void c_siphash_init(CSipHash *state, const uint8_t seed[16]) {
uint64_t k0, k1;
k0 = c_siphash_read_le64(seed);
k1 = c_siphash_read_le64(seed + 8);
*state = (CSipHash) {
/*
* Default seed is taken from the reference implementation
* of SipHash24 ("somepseudorandomlygeneratedbytes"). Callers
* are still recommended to provide proper seeds themselves.
*/
.v0 = 0x736f6d6570736575ULL ^ k0,
.v1 = 0x646f72616e646f6dULL ^ k1,
.v2 = 0x6c7967656e657261ULL ^ k0,
.v3 = 0x7465646279746573ULL ^ k1,
.padding = 0,
.n_bytes = 0,
};
}
/**
* c_siphash_append() - hash stream of data
* @state: context object
* @bytes: array of input bytes
* @n_bytes: number of input bytes
*
* This feeds an array of bytes into the SipHash state machine. This is a
* streaming-capable API. That is, the resulting hash is the same, regardless
* of the way you chunk the input.
* This function simply feeds the given bytes into the SipHash state machine.
* It does not produce a final hash. You can call this function many times to
* append more data. To retrieve the final hash, call c_siphash_finalize().
*
* Note that this implementation works best when used with chunk-sizes of
* multiples of 64bit (8-bytes). This is not a requirement, though.
*/
_public_ void c_siphash_append(CSipHash *state, const uint8_t *bytes, size_t n_bytes) {
const uint8_t *end = bytes + n_bytes;
size_t left = state->n_bytes & 7;
uint64_t m;
state->n_bytes += n_bytes;
/*
* SipHash operates on 64bit chunks. If the previous blob was not a
* multiple of 64bit in length, we must operate on single bytes.
*/
if (left > 0) {
for ( ; bytes < end && left < 8; ++bytes, ++left)
state->padding |= ((uint64_t) *bytes) << (left * 8);
if (bytes == end && left < 8)
return;
state->v3 ^= state->padding;
c_siphash_sipround(state);
c_siphash_sipround(state);
state->v0 ^= state->padding;
state->padding = 0;
}
end -= (state->n_bytes % sizeof(uint64_t));
/*
* We are now guaranteed to be at a 64bit state boundary. Hence, we can
* operate in 64bit chunks on all input. This is much faster than the
* one-byte-at-a-time loop.
*/
for ( ; bytes < end; bytes += 8) {
m = c_siphash_read_le64(bytes);
state->v3 ^= m;
c_siphash_sipround(state);
c_siphash_sipround(state);
state->v0 ^= m;
}
/*
* Now that we hashed as much 64bit chunks as possible, we need to
* remember the remaining trailing bytes. Keep them in @padding so the
* next round (or the finalizer) get access to them.
*/
left = state->n_bytes & 7;
switch (left) {
case 7:
state->padding |= ((uint64_t) bytes[6]) << 48;
/* fallthrough */
case 6:
state->padding |= ((uint64_t) bytes[5]) << 40;
/* fallthrough */
case 5:
state->padding |= ((uint64_t) bytes[4]) << 32;
/* fallthrough */
case 4:
state->padding |= ((uint64_t) bytes[3]) << 24;
/* fallthrough */
case 3:
state->padding |= ((uint64_t) bytes[2]) << 16;
/* fallthrough */
case 2:
state->padding |= ((uint64_t) bytes[1]) << 8;
/* fallthrough */
case 1:
state->padding |= ((uint64_t) bytes[0]);
/* fallthrough */
case 0:
break;
}
}
/**
* c_siphash_finalize() - finalize hash
* @state: context object
*
* This produces the final SipHash24 hash value for the given SipHash state.
* That is, it produces a hash value corresponding to the SipHash24 hash value
* of the concatenated byte-array passed into @state via c_siphash_append().
*
* Note that @state has an invalid state after this function returns. To reuse
* it for another hash, you must call c_siphash_init() again. If you don't need
* the object, anymore, you can release it any time. There is no need to
* destroy the object explicitly.
*
* Return: 64bit hash value
*/
_public_ uint64_t c_siphash_finalize(CSipHash *state) {
uint64_t b;
b = state->padding | (((uint64_t) state->n_bytes) << 56);
state->v3 ^= b;
c_siphash_sipround(state);
c_siphash_sipround(state);
state->v0 ^= b;
state->v2 ^= 0xff;
c_siphash_sipround(state);
c_siphash_sipround(state);
c_siphash_sipround(state);
c_siphash_sipround(state);
return state->v0 ^ state->v1 ^ state->v2 ^ state->v3;
}
/**
* c_siphash_hash() - hash data blob
* @seed: 128bit seed
* @bytes: byte array to hash
* @n_bytes: number of bytes to hash
*
* This produces the SipHash24 hash value for the input @bytes / @n_bytes,
* using the seed provided as @seed.
*
* This is functionally equivalent to:
*
* CSipHash state;
* c_siphash_init(&state, seed);
* c_siphash_apend(&state, bytes, n_bytes);
* return c_siphash_finalize(&state);
*
* Unlike the streaming API, this is a one-shot call suitable for any data that
* is available in-memory at the same time.
*
* Return: 64bit hash value
*/
_public_ uint64_t c_siphash_hash(const uint8_t seed[16], const uint8_t *bytes, size_t n_bytes) {
CSipHash state;
c_siphash_init(&state, seed);
c_siphash_append(&state, bytes, n_bytes);
return c_siphash_finalize(&state);
}
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