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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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9
node/Packet.hpp
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@ -92,6 +92,11 @@
*/
#define ZT_PROTO_VERB_FLAG_COMPRESSED 0x80
/**
* Rounds used for Salsa20 encryption in ZT
*/
#define ZT_PROTO_SALSA20_ROUNDS 12
// Indices of fields in normal packet header -- do not change as this
// might require both code rework and will break compatibility.
#define ZT_PACKET_IDX_IV 0
@ -852,7 +857,7 @@ public:
else (*this)[ZT_PACKET_IDX_FLAGS] &= (char)(~ZT_PROTO_FLAG_ENCRYPTED);
_mangleKey((const unsigned char *)key,mangledKey);
Salsa20 s20(mangledKey,256,field(ZT_PACKET_IDX_IV,8));
Salsa20 s20(mangledKey,256,field(ZT_PACKET_IDX_IV,8),ZT_PROTO_SALSA20_ROUNDS);
// MAC key is always the first 32 bytes of the Salsa20 key stream
// This is the same construction DJB's NaCl library uses
@ -880,7 +885,7 @@ public:
unsigned char *const payload = field(ZT_PACKET_IDX_VERB,payloadLen);
_mangleKey((const unsigned char *)key,mangledKey);
Salsa20 s20(mangledKey,256,field(ZT_PACKET_IDX_IV,8));
Salsa20 s20(mangledKey,256,field(ZT_PACKET_IDX_IV,8),ZT_PROTO_SALSA20_ROUNDS);
s20.encrypt(ZERO_KEY,macKey,sizeof(macKey));
Poly1305::compute(mac,payload,payloadLen,macKey);