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Tweak how we do crypto of the masked portions of HELLO just to be more "boring" in the DJB sense.

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This commit is contained in:
Adam Ierymenko 2017-02-06 07:39:38 -08:00
parent f85a630a64
commit 803f74634a
2 changed files with 11 additions and 7 deletions
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6
node/Packet.cpp
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@ -2026,9 +2026,11 @@ bool Packet::dearmor(const void *key)
void Packet::cryptField(const void *key,unsigned int start,unsigned int len)
{
unsigned char mangledKey[32];
uint64_t iv = Utils::hton((uint64_t)start ^ at<uint64_t>(ZT_PACKET_IDX_IV));
unsigned char macKey[32];
_salsa20MangleKey((const unsigned char *)key,mangledKey);
Salsa20 s20(mangledKey,256,&iv);
mangledKey[0] ^= 1; // slightly alter key for this use case as an added guard against key stream reuse
Salsa20 s20(mangledKey,256,field(ZT_PACKET_IDX_IV,8));
s20.crypt12(ZERO_KEY,macKey,sizeof(macKey)); // discard the first 32 bytes of key stream (the ones use for MAC in armor()) as a precaution
unsigned char *const ptr = field(start,len);
s20.crypt12(ptr,ptr,len);
}

12
node/Packet.hpp
View File

@ -1353,16 +1353,18 @@ public:
/**
* Encrypt/decrypt a separately armored portion of a packet
*
* This keys using the same key in the same way as armor/dearmor, but
* uses a different IV computed from the packet's IV plus the starting
* point index.
*
* This currently uses Salsa20/12, but any message that uses this should
* incorporate a cipher selector to permit this to be changed later.
* incorporate a cipher selector to permit this to be changed later. To
* ensure that key stream is not reused, the key is slightly altered for
* this use case and the same initial 32 keystream bytes that are taken
* for MAC in ordinary armor() are also skipped here.
*
* This is currently only used to mask portions of HELLO as an extra
* security precation since most of that message is sent in the clear.
*
* This must NEVER be used more than once in the same packet, as doing
* so will result in re-use of the same key stream.
*
* @param key 32-byte key
* @param start Start of encrypted portion
* @param len Length of encrypted portion