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nts: refactor NTS context

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Add a context structure for the algorithm and keys established by
NTS-KE. Modify the client to save the context and reset the SIV key to
the C2S/S2C key before each request/response instead of keeping two SIV
instances.

This will make it easier for the server to support different algorithms
and allow the client to save the context with cookies to disk.
This commit is contained in:
Miroslav Lichvar
2020-03-30 18:06:57 +02:00
parent 5296858411
commit adcf073484
10 changed files with 121 additions and 91 deletions
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40
nts_ke_server.c
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@@ -293,8 +293,8 @@ helper_signal(int x)
static int
prepare_response(NKSN_Instance session, int error, int next_protocol, int aead_algorithm)
{
NKE_Context context;
NKE_Cookie cookie;
NKE_Key c2s, s2c;
uint16_t datum;
int i;
@@ -329,11 +329,13 @@ prepare_response(NKSN_Instance session, int error, int next_protocol, int aead_a
return 0;
}
if (!NKSN_GetKeys(session, aead_algorithm, &c2s, &s2c))
context.algorithm = aead_algorithm;
if (!NKSN_GetKeys(session, aead_algorithm, &context.c2s, &context.s2c))
return 0;
for (i = 0; i < NKE_MAX_COOKIES; i++) {
if (!NKS_GenerateCookie(&c2s, &s2c, &cookie))
if (!NKS_GenerateCookie(&context, &cookie))
return 0;
if (!NKSN_AddRecord(session, 0, NKE_RECORD_COOKIE, cookie.cookie, cookie.length))
return 0;
@@ -679,7 +681,7 @@ NKS_Finalise(void)
/* A server cookie consists of key ID, nonce, and encrypted C2S+S2C keys */
int
NKS_GenerateCookie(NKE_Key *c2s, NKE_Key *s2c, NKE_Cookie *cookie)
NKS_GenerateCookie(NKE_Context *context, NKE_Cookie *cookie)
{
unsigned char plaintext[2 * NKE_MAX_KEY_LENGTH], *ciphertext;
int plaintext_length, tag_length;
@@ -691,8 +693,14 @@ NKS_GenerateCookie(NKE_Key *c2s, NKE_Key *s2c, NKE_Cookie *cookie)
return 0;
}
if (c2s->length < 0 || c2s->length > NKE_MAX_KEY_LENGTH ||
s2c->length < 0 || s2c->length > NKE_MAX_KEY_LENGTH) {
/* The algorithm is hardcoded for now */
if (context->algorithm != AEAD_AES_SIV_CMAC_256) {
DEBUG_LOG("Unexpected SIV algorithm");
return 0;
}
if (context->c2s.length < 0 || context->c2s.length > NKE_MAX_KEY_LENGTH ||
context->s2c.length < 0 || context->s2c.length > NKE_MAX_KEY_LENGTH) {
DEBUG_LOG("Invalid key length");
return 0;
}
@@ -705,10 +713,10 @@ NKS_GenerateCookie(NKE_Key *c2s, NKE_Key *s2c, NKE_Cookie *cookie)
header->key_id = key->id;
UTI_GetRandomBytes(header->nonce, sizeof (header->nonce));
plaintext_length = c2s->length + s2c->length;
plaintext_length = context->c2s.length + context->s2c.length;
assert(plaintext_length <= sizeof (plaintext));
memcpy(plaintext, c2s->key, c2s->length);
memcpy(plaintext + c2s->length, s2c->key, s2c->length);
memcpy(plaintext, context->c2s.key, context->c2s.length);
memcpy(plaintext + context->c2s.length, context->s2c.key, context->s2c.length);
tag_length = SIV_GetTagLength(key->siv);
cookie->length = sizeof (*header) + plaintext_length + tag_length;
@@ -729,7 +737,7 @@ NKS_GenerateCookie(NKE_Key *c2s, NKE_Key *s2c, NKE_Cookie *cookie)
/* ================================================== */
int
NKS_DecodeCookie(NKE_Cookie *cookie, NKE_Key *c2s, NKE_Key *s2c)
NKS_DecodeCookie(NKE_Cookie *cookie, NKE_Context *context)
{
unsigned char plaintext[2 * NKE_MAX_KEY_LENGTH], *ciphertext;
int ciphertext_length, plaintext_length, tag_length;
@@ -776,12 +784,14 @@ NKS_DecodeCookie(NKE_Cookie *cookie, NKE_Key *c2s, NKE_Key *s2c)
return 0;
}
c2s->length = plaintext_length / 2;
s2c->length = plaintext_length / 2;
assert(c2s->length <= sizeof (c2s->key));
context->algorithm = AEAD_AES_SIV_CMAC_256;
memcpy(c2s->key, plaintext, c2s->length);
memcpy(s2c->key, plaintext + c2s->length, s2c->length);
context->c2s.length = plaintext_length / 2;
context->s2c.length = plaintext_length / 2;
assert(context->c2s.length <= sizeof (context->c2s.key));
memcpy(context->c2s.key, plaintext, context->c2s.length);
memcpy(context->s2c.key, plaintext + context->c2s.length, context->s2c.length);
return 1;
}