Post by Chet RameyPost by Ole Tange'brand' in variables.c is comparable in size to ChaCha20 and ChaCha20
https://en.wikipedia.org/wiki/Salsa20
Could we please replace 'brand' with ChaCha20?
What is your application that you need something more complicated than
the existing PRNG?
I do not have that currently, but it seems like a fairly small change
and it seems odd to have modern software not use modern algorithms.
Git's use of SHA1 seems to be a prime example of what can go wrong:
https://shattered.io/
If you look at the code it is really not much bigger:
#define ROTL(a,b) (((a) << (b)) | ((a) >> (32 - (b))))
#define QR(a, b, c, d) ( \
a += b, d ^= a, d = ROTL(d,16), \
c += d, b ^= c, b = ROTL(b,12), \
a += b, d ^= a, d = ROTL(d, 8), \
c += d, b ^= c, b = ROTL(b, 7))
#define ROUNDS 20
void chacha_block(uint32_t out[16], uint32_t const in[16])
{
int i;
uint32_t x[16];
for (i = 0; i < 16; ++i)
x[i] = in[i];
// 10 loops × 2 rounds/loop = 20 rounds
for (i = 0; i < ROUNDS; i += 2) {
// Odd round
QR(x[0], x[4], x[ 8], x[12]); // column 0
QR(x[1], x[5], x[ 9], x[13]); // column 1
QR(x[2], x[6], x[10], x[14]); // column 2
QR(x[3], x[7], x[11], x[15]); // column 3
// Even round
QR(x[0], x[5], x[10], x[15]); // diagonal 1 (main diagonal)
QR(x[1], x[6], x[11], x[12]); // diagonal 2
QR(x[2], x[7], x[ 8], x[13]); // diagonal 3
QR(x[3], x[4], x[ 9], x[14]); // diagonal 4
}
for (i = 0; i < 16; ++i)
out[i] = x[i] + in[i];
}
Can you elaborate on why you think it is a bad idea to change an
insecure PRNG into a non-broken one?
/Ole