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Make Salsa20 variable-round, allowing for Salsa20/12 to be used for Packet encrypt and decrypt. Profiling analysis found that Salsa20 encrypt was accounting for a nontrivial percentage of CPU time, so it makes sense to cut this load fundamentally. There are no published attacks against Salsa20/12, and DJB believes 20 rounds to be overkill. This should be more than enough for our needs. Obviously incorporating ASM Salsa20 is among the next steps for performance.

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This commit is contained in:
Adam Ierymenko 2013-10-18 17:39:48 -04:00
parent 37e3bc3467
commit 8c9b73f67b
7 changed files with 41 additions and 14 deletions
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7
node/Salsa20.cpp
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@ -29,7 +29,7 @@ namespace ZeroTier {
static const char *sigma = "expand 32-byte k";
static const char *tau = "expand 16-byte k";
void Salsa20::init(const void *key,unsigned int kbits,const void *iv)
void Salsa20::init(const void *key,unsigned int kbits,const void *iv,unsigned int rounds)
throw()
{
const char *constants;
@ -59,6 +59,8 @@ void Salsa20::init(const void *key,unsigned int kbits,const void *iv)
_state[5] = U8TO32_LITTLE(constants + 4);
_state[10] = U8TO32_LITTLE(constants + 8);
_state[15] = U8TO32_LITTLE(constants + 12);
_roundsDiv2 = rounds / 2;
}
void Salsa20::encrypt(const void *in,void *out,unsigned int bytes)
@ -114,7 +116,8 @@ void Salsa20::encrypt(const void *in,void *out,unsigned int bytes)
x13 = j13;
x14 = j14;
x15 = j15;
for (i = 20;i > 0;i -= 2) {
//for (i = 20;i > 0;i -= 2) {
for(i=0;i<_roundsDiv2;++i) {
x4 = XOR( x4,ROTATE(PLUS( x0,x12), 7));
x8 = XOR( x8,ROTATE(PLUS( x4, x0), 9));
x12 = XOR(x12,ROTATE(PLUS( x8, x4),13));