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Improve ciphersuite order stability when disabling ciphersuites.

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Change ssl_create_cipher_list() to prefer ephemeral ECDH over
ephemeral DH.
This commit is contained in:
Bodo Möller 2007-02-20 16:36:58 +00:00
parent e041863905
commit fd5bc65cc8
2 changed files with 98 additions and 20 deletions
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21
CHANGES
View file

@ -4,6 +4,27 @@
Changes between 0.9.8e and 0.9.9 [xx XXX xxxx]
*) Change ssl_cipher_apply_rule(), the internal function that does
the work each time a ciphersuite string requests enabling
("foo+bar"), moving ("+foo+bar"), disabling ("-foo+bar", or
removing ("!foo+bar") a class of ciphersuites: Now it maintains
the order of disabled ciphersuites such that those ciphersuites
that most recently went from enabled to disabled not only stay
in order with respect to each other, but also have higher priority
than other disabled ciphersuites the next time ciphersuites are
enabled again.
This means that you can now say, e.g., "PSK:-PSK:HIGH" to enable
the same ciphersuites as with "HIGH" alone, but in a specific
order where the PSK ciphersuites come first (since they are the
most recently disabled ciphersuites when "HIGH" is parsed).
Also, change ssl_create_cipher_list() (using this new
funcionality) such that between otherwise identical
cihpersuites, ephemeral ECDH is preferred over ephemeral DH in
the default order.
[Bodo Moeller]
*) Change ssl_create_cipher_list() so that it automatically
arranges the ciphersuites in reasonable order before starting
to process the rule string. Thus, the definition for "DEFAULT"

97
ssl/ssl_ciph.c
View file

@ -476,7 +476,7 @@ static void ll_append_tail(CIPHER_ORDER **head, CIPHER_ORDER *curr,
*head=curr->next;
if (curr->prev != NULL)
curr->prev->next=curr->next;
if (curr->next != NULL) /* should always be true */
if (curr->next != NULL)
curr->next->prev=curr->prev;
(*tail)->next=curr;
curr->prev= *tail;
@ -484,6 +484,22 @@ static void ll_append_tail(CIPHER_ORDER **head, CIPHER_ORDER *curr,
*tail=curr;
}
static void ll_append_head(CIPHER_ORDER **head, CIPHER_ORDER *curr,
CIPHER_ORDER **tail)
{
if (curr == *head) return;
if (curr == *tail)
*tail=curr->prev;
if (curr->next != NULL)
curr->next->prev=curr->prev;
if (curr->prev != NULL)
curr->prev->next=curr->next;
(*head)->prev=curr;
curr->next= *head;
curr->prev=NULL;
*head=curr;
}
static void ssl_cipher_get_disabled(unsigned long *mkey, unsigned long *auth, unsigned long *enc, unsigned long *mac, unsigned long *ssl)
{
*mkey = 0;
@ -586,19 +602,27 @@ static void ssl_cipher_collect_ciphers(const SSL_METHOD *ssl_method,
/*
* Prepare linked list from list entries
*/
for (i = 1; i < co_list_num - 1; i++)
{
co_list[i].prev = &(co_list[i-1]);
co_list[i].next = &(co_list[i+1]);
}
if (co_list_num > 0)
{
(*head_p) = &(co_list[0]);
(*head_p)->prev = NULL;
(*head_p)->next = &(co_list[1]);
(*tail_p) = &(co_list[co_list_num - 1]);
(*tail_p)->prev = &(co_list[co_list_num - 2]);
(*tail_p)->next = NULL;
co_list[0].prev = NULL;
if (co_list_num > 1)
{
co_list[0].next = &co_list[1];
for (i = 1; i < co_list_num - 1; i++)
{
co_list[i].prev = &co_list[i - 1];
co_list[i].next = &co_list[i + 1];
}
co_list[co_list_num - 1].prev = &co_list[co_list_num - 2];
}
co_list[co_list_num - 1].next = NULL;
*head_p = &co_list[0];
*tail_p = &co_list[co_list_num - 1];
}
}
@ -679,22 +703,38 @@ static void ssl_cipher_apply_rule(unsigned long cipher_id,
int rule, int strength_bits,
CIPHER_ORDER **head_p, CIPHER_ORDER **tail_p)
{
CIPHER_ORDER *head, *tail, *curr, *curr2, *tail2;
CIPHER_ORDER *head, *tail, *curr, *curr2, *last;
SSL_CIPHER *cp;
int reverse = 0;
#ifdef CIPHER_DEBUG
printf("Applying rule %d with %08lx/%08lx/%08lx/%08lx/%08lx %08lx (%d)\n",
rule, alg_mkey, alg_auth, alg_enc, alg_mac, alg_ssl, algo_strength, strength_bits);
#endif
curr = head = *head_p;
curr2 = head;
tail2 = tail = *tail_p;
if (rule == CIPHER_DEL)
reverse = 1; /* needed to maintain sorting between currently deleted ciphers */
head = *head_p;
tail = *tail_p;
if (reverse)
{
curr = tail;
last = head;
}
else
{
curr = head;
last = tail;
}
curr2 = curr;
for (;;)
{
if ((curr == NULL) || (curr == tail2)) break;
if ((curr == NULL) || (curr == last)) break;
curr = curr2;
curr2 = curr->next;
curr2 = reverse ? curr->prev : curr->next;
cp = curr->cipher;
@ -736,6 +776,7 @@ static void ssl_cipher_apply_rule(unsigned long cipher_id,
/* add the cipher if it has not been added yet. */
if (rule == CIPHER_ADD)
{
/* reverse == 0 */
if (!curr->active)
{
ll_append_tail(&head, curr, &tail);
@ -745,15 +786,27 @@ static void ssl_cipher_apply_rule(unsigned long cipher_id,
/* Move the added cipher to this location */
else if (rule == CIPHER_ORD)
{
/* reverse == 0 */
if (curr->active)
{
ll_append_tail(&head, curr, &tail);
}
}
else if (rule == CIPHER_DEL)
curr->active = 0;
{
/* reverse == 1 */
if (curr->active)
{
/* most recently deleted ciphersuites get best positions
* for any future CIPHER_ADD (note that the CIPHER_DEL loop
* works in reverse to maintain the order) */
ll_append_head(&head, curr, &tail);
curr->active = 0;
}
}
else if (rule == CIPHER_KILL)
{
/* reverse == 0 */
if (head == curr)
head = curr->next;
else
@ -1123,7 +1176,11 @@ STACK_OF(SSL_CIPHER) *ssl_create_cipher_list(const SSL_METHOD *ssl_method,
/* Now arrange all ciphers by preference: */
/* Temporarily enabled AES first (preferred cipher) */
/* Everything else being equal, prefer ephemeral ECDH over other key exchange mechanisms */
ssl_cipher_apply_rule(0, SSL_kEECDH, 0, 0, 0, 0, 0, CIPHER_ADD, -1, &head, &tail);
ssl_cipher_apply_rule(0, SSL_kEECDH, 0, 0, 0, 0, 0, CIPHER_DEL, -1, &head, &tail);
/* Temporarily enable AES first (preferred cipher) */
ssl_cipher_apply_rule(0, 0, 0, SSL_AES, 0, 0, 0, CIPHER_ADD, -1, &head, &tail);
/* Temporarily enable everything else */