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prf-plus: Fail after counter has wrapped around

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The behavior is undefined if this happens (RFC 7296, section 2.13).
Instead of switching to the non-counter mode, or letting the counter
wrap, this makes it clear that the usage was not as intended.
This commit is contained in:
Tobias Brunner
2019-10-21 13:53:11 +02:00
parent c75010080a
commit 768e013790
4 changed files with 206 additions and 37 deletions
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src/libstrongswan/crypto/prf_plus.c
+43 -36
View File
@@ -20,6 +20,8 @@
typedef struct private_prf_plus_t private_prf_plus_t;
typedef bool (*apply_prf_t)(private_prf_plus_t *this);
/**
* Private data of an prf_plus_t object.
*
@@ -42,7 +44,7 @@ struct private_prf_plus_t {
chunk_t seed;
/**
* Octet which will be appended to the seed, 0 if not used
* Octet which will be appended to the seed if a counter is used.
*/
uint8_t counter;
@@ -55,8 +57,41 @@ struct private_prf_plus_t {
* Buffer to store current PRF result.
*/
chunk_t buffer;
/**
* The prf application method depending on whether a counter is used.
*/
apply_prf_t apply_prf;
};
/**
* Apply the PRF using the running counter
*/
static bool apply_prf_counter(private_prf_plus_t *this)
{
if (!this->prf->get_bytes(this->prf, this->seed, NULL) ||
!this->prf->get_bytes(this->prf, chunk_from_thing(this->counter),
this->buffer.ptr))
{
return FALSE;
}
this->counter++;
if (!this->counter)
{ /* according to RFC 7296, section 2.13, prf+ is undefined once the
* counter wrapped, so let's fail for future calls */
this->apply_prf = (void*)return_false;
}
return TRUE;
}
/**
* Apply the PRF using the running counter
*/
static bool apply_prf(private_prf_plus_t *this)
{
return this->prf->get_bytes(this->prf, this->seed, this->buffer.ptr);
}
METHOD(prf_plus_t, get_bytes, bool,
private_prf_plus_t *this, size_t length, uint8_t *buffer)
{
@@ -70,23 +105,9 @@ METHOD(prf_plus_t, get_bytes, bool,
{
return FALSE;
}
if (this->counter)
if (!this->apply_prf(this))
{
if (!this->prf->get_bytes(this->prf, this->seed, NULL) ||
!this->prf->get_bytes(this->prf,
chunk_from_thing(this->counter), this->buffer.ptr))
{
return FALSE;
}
this->counter++;
}
else
{
if (!this->prf->get_bytes(this->prf, this->seed,
this->buffer.ptr))
{
return FALSE;
}
return FALSE;
}
this->used = 0;
}
@@ -136,28 +157,14 @@ prf_plus_t *prf_plus_create(prf_t *prf, bool counter, chunk_t seed)
.prf = prf,
.seed = chunk_clone(seed),
.buffer = chunk_alloc(prf->get_block_size(prf)),
.apply_prf = counter ? apply_prf_counter : apply_prf,
.counter = 0x01,
);
if (counter)
if (!this->apply_prf(this))
{
this->counter = 0x01;
if (!this->prf->get_bytes(this->prf, this->seed, NULL) ||
!this->prf->get_bytes(this->prf, chunk_from_thing(this->counter),
this->buffer.ptr))
{
destroy(this);
return NULL;
}
this->counter++;
destroy(this);
return NULL;
}
else
{
if (!this->prf->get_bytes(this->prf, this->seed, this->buffer.ptr))
{
destroy(this);
return NULL;
}
}
return &this->public;
}