##### https://github.com/mupq/pqm4
Tip revision: ae06d3d
fips202.c
``````/* Based on the public domain implementation in
* crypto_hash/keccakc512/simple/ from http://bench.cr.yp.to/supercop.html
* by Ronny Van Keer
* and the public domain "TweetFips202" implementation
* by Gilles Van Assche, Daniel J. Bernstein, and Peter Schwabe */

#include <stdint.h>
#include <string.h>
#include "fips202.h"
#include "keccakf1600.h"

#define NROUNDS 24
#define ROL(a, offset) ((a << offset) ^ (a >> (64-offset)))
#define MIN(a, b) ((a) < (b) ? (a) : (b))

/*************************************************
* Name:        keccak_absorb
*
* Description: Absorb step of Keccak;
*              non-incremental, starts by zeroeing the state.
*
* Arguments:   - uint64_t *s:             pointer to (uninitialized) output Keccak state
*              - unsigned int r:          rate in bytes (e.g., 168 for SHAKE128)
*              - const unsigned char *m:  pointer to input to be absorbed into s
*              - unsigned long long mlen: length of input in bytes
*              - unsigned char p:         domain-separation byte for different Keccak-derived functions
**************************************************/
static void keccak_absorb(uint64_t *s,
unsigned int r,
const unsigned char *m, unsigned long long int mlen,
unsigned char p)
{
unsigned long long i;
unsigned char t[200];

while (mlen >= r)
{
KeccakF1600_StateXORBytes(s, m, 0, r);
KeccakF1600_StatePermute(s);
mlen -= r;
m += r;
}

for (i = 0; i < r; ++i)
t[i] = 0;
for (i = 0; i < mlen; ++i)
t[i] = m[i];
t[i] = p;
t[r - 1] |= 128;

KeccakF1600_StateXORBytes(s, t, 0, r);
}

/*************************************************
* Name:        keccak_squeezeblocks
*
* Description: Squeeze step of Keccak. Squeezes full blocks of r bytes each.
*              Modifies the state. Can be called multiple times to keep squeezing,
*              i.e., is incremental.
*
* Arguments:   - unsigned char *h:               pointer to output blocks
*              - unsigned long long int nblocks: number of blocks to be squeezed (written to h)
*              - uint64_t *s:                    pointer to in/output Keccak state
*              - unsigned int r:                 rate in bytes (e.g., 168 for SHAKE128)
**************************************************/
static void keccak_squeezeblocks(unsigned char *h, unsigned long long int nblocks,
uint64_t *s,
unsigned int r)
{
while(nblocks > 0)
{
KeccakF1600_StatePermute(s);
KeccakF1600_StateExtractBytes(s, h, 0, r);
h += r;
nblocks--;
}
}

/********** cSHAKE128 ***********/

void cshake128_simple_absorb(uint64_t s[25], uint16_t cstm, const unsigned char *in, unsigned long long inlen)
{
unsigned char sep[8];
unsigned int i;

for (i = 0; i < 25; i++)
s[i] = 0;

/* Absorb customization (domain-separation) string */
sep[0] = 0x01;
sep[1] = 0xa8;
sep[2] = 0x01;
sep[3] = 0x00;
sep[4] = 0x01;
sep[5] = 16; // fixed bitlen of cstm
sep[6] = cstm & 0xff;
sep[7] = cstm >> 8;

KeccakF1600_StateXORBytes(s, sep, 0, 8);
KeccakF1600_StatePermute(s);

/* Absorb input */
keccak_absorb(s, SHAKE128_RATE, in, inlen, 0x04);
}

void cshake128_simple_squeezeblocks(unsigned char *output, unsigned long long nblocks, uint64_t *s)
{
keccak_squeezeblocks(output, nblocks, s, SHAKE128_RATE);
}

void cshake128_simple(unsigned char *output, unsigned long long outlen, uint16_t cstm, const unsigned char *in, unsigned long long inlen)
{
uint64_t s[25];
unsigned char t[SHAKE128_RATE];
unsigned int i;

cshake128_simple_absorb(s, cstm, in, inlen);

/* Squeeze output */
keccak_squeezeblocks(output, outlen/SHAKE128_RATE, s, SHAKE128_RATE);
output += (outlen/SHAKE128_RATE)*SHAKE128_RATE;

if (outlen%SHAKE128_RATE)
{
keccak_squeezeblocks(t, 1, s, SHAKE128_RATE);
for (i = 0; i < outlen%SHAKE128_RATE; i++)
output[i] = t[i];
}
}

/*************************************************
* Name:        shake128_absorb
*
* Description: Absorb step of the SHAKE128 XOF.
*              non-incremental, starts by zeroeing the state.
*
* Arguments:   - uint64_t *s:                     pointer to (uninitialized) output Keccak state
*              - const unsigned char *input:      pointer to input to be absorbed into s
*              - unsigned long long inputByteLen: length of input in bytes
**************************************************/
void shake128_absorb(uint64_t *s, const unsigned char *input, unsigned int inputByteLen)
{
int i;
for (i = 0; i < 25; i++)
s[i] = 0;

keccak_absorb(s, SHAKE128_RATE, input, inputByteLen, 0x1F);
}

/*************************************************
* Name:        shake128_squeezeblocks
*
* Description: Squeeze step of SHAKE128 XOF. Squeezes full blocks of SHAKE128_RATE bytes each.
*              Modifies the state. Can be called multiple times to keep squeezing,
*              i.e., is incremental.
*
* Arguments:   - unsigned char *output:      pointer to output blocks
*              - unsigned long long nblocks: number of blocks to be squeezed (written to output)
*              - uint64_t *s:                pointer to in/output Keccak state
**************************************************/
void shake128_squeezeblocks(unsigned char *output, unsigned long long nblocks, uint64_t *s)
{
keccak_squeezeblocks(output, nblocks, s, SHAKE128_RATE);
}

void shake128(unsigned char *output, unsigned long long outlen, const unsigned char *input, unsigned long long inlen)
{
uint64_t s[25] = {0};
unsigned char t[SHAKE128_RATE];
unsigned long long nblocks = outlen/SHAKE128_RATE;
size_t i;

/* Absorb input */
keccak_absorb(s, SHAKE128_RATE, input, inlen, 0x1F);

/* Squeeze output */
keccak_squeezeblocks(output, nblocks, s, SHAKE128_RATE);

output += nblocks*SHAKE128_RATE;
outlen -= nblocks*SHAKE128_RATE;

if (outlen)
{
keccak_squeezeblocks(t, 1, s, SHAKE128_RATE);
for (i = 0; i < outlen; i++)
output[i] = t[i];
}
}

void shake256_absorb(uint64_t *s, const unsigned char *input, unsigned int inputByteLen)
{
int i;
for (i = 0; i < 25; i++)
s[i] = 0;

keccak_absorb(s, SHAKE256_RATE, input, inputByteLen, 0x1F);
}

void shake256_squeezeblocks(unsigned char *output, unsigned long long nblocks, uint64_t *s)
{
keccak_squeezeblocks(output, nblocks, s, SHAKE256_RATE);
}

/*************************************************
* Name:        shake256
*
* Description: SHAKE256 XOF with non-incremental API
*
* Arguments:   - unsigned char *output:      pointer to output
*              - unsigned long long outlen:  requested output length in bytes
- const unsigned char *input: pointer to input
- unsigned long long inlen:   length of input in bytes
**************************************************/
void shake256(unsigned char *output, unsigned long long outlen,
const unsigned char *input, unsigned long long inlen)
{
uint64_t s[25] = {0};
unsigned char t[SHAKE256_RATE];
unsigned long long nblocks = outlen/SHAKE256_RATE;
size_t i;

/* Absorb input */
keccak_absorb(s, SHAKE256_RATE, input, inlen, 0x1F);

/* Squeeze output */
keccak_squeezeblocks(output, nblocks, s, SHAKE256_RATE);

output+=nblocks*SHAKE256_RATE;
outlen-=nblocks*SHAKE256_RATE;

if(outlen)
{
keccak_squeezeblocks(t, 1, s, SHAKE256_RATE);
for(i=0;i<outlen;i++)
output[i] = t[i];
}
}

/*************************************************
* Name:        sha3_256
*
* Description: SHA3-256 with non-incremental API
*
* Arguments:   - unsigned char *output:      pointer to output
*              - const unsigned char *input: pointer to input
*              - unsigned long long inlen:   length of input in bytes
**************************************************/
void sha3_256(unsigned char *output, const unsigned char *input, unsigned long long inlen)
{
uint64_t s[25] = {0};
unsigned char t[SHA3_256_RATE];
size_t i;

/* Absorb input */
keccak_absorb(s, SHA3_256_RATE, input, inlen, 0x06);

/* Squeeze output */
keccak_squeezeblocks(t, 1, s, SHA3_256_RATE);

for(i=0;i<32;i++)
output[i] = t[i];
}

/*************************************************
* Name:        sha3_512
*
* Description: SHA3-512 with non-incremental API
*
* Arguments:   - unsigned char *output:      pointer to output
*              - const unsigned char *input: pointer to input
*              - unsigned long long inlen:   length of input in bytes
**************************************************/
void sha3_512(unsigned char *output, const unsigned char *input, unsigned long long inlen)
{
uint64_t s[25] = {0};
unsigned char t[SHA3_512_RATE];
size_t i;

/* Absorb input */
keccak_absorb(s, SHA3_512_RATE, input, inlen, 0x06);

/* Squeeze output */
keccak_squeezeblocks(t, 1, s, SHA3_512_RATE);

for(i=0;i<64;i++)
output[i] = t[i];
}

/********** cSHAKE256 ***********/

void cshake256_simple_absorb(uint64_t s[25], uint16_t cstm, const unsigned char *in, unsigned long long inlen)
{
unsigned char sep[8];
unsigned int i;

for (i = 0; i < 25; i++)
s[i] = 0;

/* Absorb customization (domain-separation) string */
sep[0] = 0x01;
sep[1] = 0x88;
sep[2] = 0x01;
sep[3] = 0x00;
sep[4] = 0x01;
sep[5] = 16; // fixed bitlen of cstm
sep[6] = cstm & 0xff;
sep[7] = cstm >> 8;

KeccakF1600_StateXORBytes(s, sep, 0, 8);
KeccakF1600_StatePermute(s);

/* Absorb input */
keccak_absorb(s, SHAKE256_RATE, in, inlen, 0x04);
}

void cshake256_simple_squeezeblocks(unsigned char *output, unsigned long long nblocks, uint64_t *s)
{
keccak_squeezeblocks(output, nblocks, s, SHAKE256_RATE);
}

void cshake256_simple(unsigned char *output, unsigned long long outlen, uint16_t cstm, const unsigned char *in, unsigned long long inlen)
{
uint64_t s[25];
unsigned char t[SHAKE256_RATE];
unsigned int i;

cshake256_simple_absorb(s, cstm, in, inlen);

/* Squeeze output */
keccak_squeezeblocks(output, outlen/SHAKE256_RATE, s, SHAKE256_RATE);
output += (outlen/SHAKE256_RATE)*SHAKE256_RATE;

if(outlen%SHAKE256_RATE)
{
keccak_squeezeblocks(t, 1, s, SHAKE256_RATE);
for (i = 0; i < outlen%SHAKE256_RATE; i++)
output[i] = t[i];
}
}
``````