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optimal padding for one-time messages

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orignal 2021-07-23 20:28:55 -04:00
parent c7234f705a
commit 26d5ced2ef
1 changed files with 18 additions and 8 deletions
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26
libi2pd/ECIESX25519AEADRatchetSession.cpp
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@ -1104,7 +1104,8 @@ namespace garlic
return true; return true;
} }
static size_t CreateGarlicPayload (std::shared_ptr<const I2NPMessage> msg, uint8_t * payload, bool datetime) static size_t CreateGarlicPayload (std::shared_ptr<const I2NPMessage> msg, uint8_t * payload,
bool datetime, size_t optimalSize)
{ {
size_t len = 0; size_t len = 0;
if (datetime) if (datetime)
@ -1129,11 +1130,20 @@ namespace garlic
len += cloveSize + 3; len += cloveSize + 3;
payload += cloveSize; payload += cloveSize;
// padding // padding
uint8_t paddingSize = rand () & 0x0F; // 0 - 15 int delta = (int)optimalSize - (int)len;
payload[0] = eECIESx25519BlkPadding; if (delta < 0 || delta > 3) // don't create padding if we are close to optimal size
htobe16buf (payload + 1, paddingSize); {
if (paddingSize) memset (payload + 3, 0, paddingSize); uint8_t paddingSize = rand () & 0x0F; // 0 - 15
len += paddingSize + 3; if (delta > 3)
{
delta -= 3;
if (paddingSize > delta) paddingSize %= delta;
}
payload[0] = eECIESx25519BlkPadding;
htobe16buf (payload + 1, paddingSize);
if (paddingSize) memset (payload + 3, 0, paddingSize);
len += paddingSize + 3;
}
return len; return len;
} }
@ -1145,7 +1155,7 @@ namespace garlic
size_t offset = 0; size_t offset = 0;
memcpy (buf + offset, &tag, 8); offset += 8; memcpy (buf + offset, &tag, 8); offset += 8;
auto payload = buf + offset; auto payload = buf + offset;
size_t len = CreateGarlicPayload (msg, payload, false); size_t len = CreateGarlicPayload (msg, payload, false, 956); // 1003 - 8 tag - 16 Poly1305 hash - 16 I2NP header - 4 garlic length - 3 local tunnel delivery
uint8_t nonce[12]; uint8_t nonce[12];
memset (nonce, 0, 12); // n = 0 memset (nonce, 0, 12); // n = 0
if (!i2p::crypto::AEADChaCha20Poly1305 (payload, len, buf, 8, key, nonce, payload, len + 16, true)) // encrypt if (!i2p::crypto::AEADChaCha20Poly1305 (payload, len, buf, 8, key, nonce, payload, len + 16, true)) // encrypt
@ -1181,7 +1191,7 @@ namespace garlic
} }
noiseState.MixKey (sharedSecret); noiseState.MixKey (sharedSecret);
auto payload = buf + offset; auto payload = buf + offset;
size_t len = CreateGarlicPayload (msg, payload, true); size_t len = CreateGarlicPayload (msg, payload, true, 900); // 1003 - 32 eph key - 16 Poly1305 hash - 16 I2NP header - 4 garlic length - 35 router tunnel delivery
uint8_t nonce[12]; uint8_t nonce[12];
memset (nonce, 0, 12); memset (nonce, 0, 12);
// encrypt payload // encrypt payload