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Simplify TLS 1.2 session ID logic

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Optimize entropy use. Only generate the exact amount of random data that we will actually keep.

Refactor done as part of work on ZD18822
This commit is contained in:
Juliusz Sosinowicz
2024-10-22 10:55:15 +02:00
parent 846ef1570d
commit 2847cbfbad
1 changed files with 42 additions and 45 deletions
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87
src/internal.c
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@@ -34510,6 +34510,29 @@ static int DoSessionTicket(WOLFSSL* ssl, const byte* input, word32* inOutIdx,
#ifndef WOLFSSL_NO_TLS12
static int getSessionID(WOLFSSL* ssl)
{
int sessIdSz = 0;
(void)ssl;
#ifndef NO_SESSION_CACHE
/* if no session cache don't send a session ID */
if (!ssl->options.sessionCacheOff)
sessIdSz = ID_LEN;
#endif
#ifdef HAVE_SESSION_TICKET
/* we may be echoing an ID as part of session tickets */
if (ssl->options.useTicket) {
/* echo session id sz can be 0,32 or bogus len in between */
sessIdSz = ssl->arrays->sessionIDSz;
if (sessIdSz > ID_LEN) {
WOLFSSL_MSG("Bad bogus session id len");
return BUFFER_ERROR;
}
}
#endif /* HAVE_SESSION_TICKET */
return sessIdSz;
}
/* handle generation of server_hello (2) */
int SendServerHello(WOLFSSL* ssl)
{
@@ -34518,17 +34541,18 @@ static int DoSessionTicket(WOLFSSL* ssl, const byte* input, word32* inOutIdx,
word16 length;
word32 idx = RECORD_HEADER_SZ + HANDSHAKE_HEADER_SZ;
int sendSz;
byte sessIdSz = ID_LEN;
#if defined(HAVE_TLS_EXTENSIONS) && defined(HAVE_SESSION_TICKET)
byte echoId = 0; /* ticket echo id flag */
#endif
byte cacheOff = 0; /* session cache off flag */
byte sessIdSz;
WOLFSSL_START(WC_FUNC_SERVER_HELLO_SEND);
WOLFSSL_ENTER("SendServerHello");
ret = getSessionID(ssl);
if (ret < 0)
return ret;
sessIdSz = (byte)ret;
length = VERSION_SZ + RAN_LEN
+ ID_LEN + ENUM_LEN
+ ENUM_LEN + sessIdSz
+ SUITE_LEN
+ ENUM_LEN;
@@ -34536,45 +34560,12 @@ static int DoSessionTicket(WOLFSSL* ssl, const byte* input, word32* inOutIdx,
ret = TLSX_GetResponseSize(ssl, server_hello, &length);
if (ret != 0)
return ret;
#ifdef HAVE_SESSION_TICKET
if (ssl->options.useTicket) {
/* echo session id sz can be 0,32 or bogus len in between */
sessIdSz = ssl->arrays->sessionIDSz;
if (sessIdSz > ID_LEN) {
WOLFSSL_MSG("Bad bogus session id len");
return BUFFER_ERROR;
}
if (!IsAtLeastTLSv1_3(ssl->version))
length -= (ID_LEN - sessIdSz); /* adjust ID_LEN assumption */
echoId = 1;
}
#endif /* HAVE_SESSION_TICKET */
#else
if (ssl->options.haveEMS) {
length += HELLO_EXT_SZ_SZ + HELLO_EXT_SZ;
}
#endif
/* is the session cache off at build or runtime */
#ifdef NO_SESSION_CACHE
cacheOff = 1;
#else
if (ssl->options.sessionCacheOff == 1) {
cacheOff = 1;
}
#endif
/* if no session cache don't send a session ID unless we're echoing
* an ID as part of session tickets */
if (cacheOff == 1
#if defined(HAVE_TLS_EXTENSIONS) && defined(HAVE_SESSION_TICKET)
&& echoId == 0
#endif
) {
length -= ID_LEN; /* adjust ID_LEN assumption */
sessIdSz = 0;
}
sendSz = length + HANDSHAKE_HEADER_SZ + RECORD_HEADER_SZ;
#ifdef WOLFSSL_DTLS
if (ssl->options.dtls) {
@@ -34605,11 +34596,7 @@ static int DoSessionTicket(WOLFSSL* ssl, const byte* input, word32* inOutIdx,
/* then random and session id */
if (!ssl->options.resuming) {
/* generate random part and session id */
ret = wc_RNG_GenerateBlock(ssl->rng, output + idx,
RAN_LEN + sizeof(sessIdSz) + sessIdSz);
if (ret != 0)
return ret;
word32 genRanLen = RAN_LEN;
#ifdef WOLFSSL_TLS13
if (TLSv1_3_Capable(ssl)) {
@@ -34617,6 +34604,7 @@ static int DoSessionTicket(WOLFSSL* ssl, const byte* input, word32* inOutIdx,
XMEMCPY(output + idx + RAN_LEN - (TLS13_DOWNGRADE_SZ + 1),
tls13Downgrade, TLS13_DOWNGRADE_SZ);
output[idx + RAN_LEN - 1] = (byte)IsAtLeastTLSv1_2(ssl);
genRanLen -= TLS13_DOWNGRADE_SZ + 1;
}
else
#endif
@@ -34628,12 +34616,21 @@ static int DoSessionTicket(WOLFSSL* ssl, const byte* input, word32* inOutIdx,
XMEMCPY(output + idx + RAN_LEN - (TLS13_DOWNGRADE_SZ + 1),
tls13Downgrade, TLS13_DOWNGRADE_SZ);
output[idx + RAN_LEN - 1] = 0;
genRanLen -= TLS13_DOWNGRADE_SZ + 1;
}
/* store info in SSL for later */
/* generate random part */
ret = wc_RNG_GenerateBlock(ssl->rng, output + idx, genRanLen);
if (ret != 0)
return ret;
XMEMCPY(ssl->arrays->serverRandom, output + idx, RAN_LEN);
idx += RAN_LEN;
/* generate session id */
output[idx++] = sessIdSz;
ret = wc_RNG_GenerateBlock(ssl->rng, output + idx, sessIdSz);
if (ret != 0)
return ret;
XMEMCPY(ssl->arrays->sessionID, output + idx, sessIdSz);
ssl->arrays->sessionIDSz = sessIdSz;
}