[asterisk-users] Need stronger SRTP ciphers (256 bit)

[Kevin Long]

Hi folks,


At least several endpoints (soft phone and desk phones) are supporting various 256 bit ciphers for SRTP these days. I *believe* libsrtp has been updated to allow this, and that only the code in Asterisk has not been been updated to allow these stronger ciphers.

Would anyone with the know-how be willing/able to submit a patch ?


Thank you,

Kevin Long

[Kevin Long]

Some more information (would love some thoughts on this, I have never submitted a patch yet).

Groundwire (Popular SIP app) supports the following cipher suites for SRTP:


AES_CM_128_HMAC_SHA1_32
AES_CM_128_HMAC_SHA1_80
AES_CM_192_HMAC_SHA1_32
AES_CM_192_HMAC_SHA1_80
AES_CM_256_HMAC_SHA1_32
AES_CM_256_HMAC_SHA1_80
AEAD_AES_128_GCM
AEAD_AES_256_GCM



I see in the asterisk 13.9.1 source tarsal, in res/res_srtp.c :


Could adding support for the above cipher suites be as simple as adding more options to this switch/case statement with the appropriate parameters or is there more to it?

Thank you!



static int policy_set_suite(crypto_policy_t *p, enum ast_srtp_suite suite)
{
switch (suite) {
case AST_AES_CM_128_HMAC_SHA1_80:
p->cipher_type = AES_128_ICM;
p->cipher_key_len = 30;
p->auth_type = HMAC_SHA1;
p->auth_key_len = 20;
p->auth_tag_len = 10;
p->sec_serv = sec_serv_conf_and_auth;
return 0;

case AST_AES_CM_128_HMAC_SHA1_32:
p->cipher_type = AES_128_ICM;
p->cipher_key_len = 30;
p->auth_type = HMAC_SHA1;
p->auth_key_len = 20;
p->auth_tag_len = 4;
p->sec_serv = sec_serv_conf_and_auth;
return 0;

default:
ast_log(LOG_ERROR, "Invalid crypto suite: %u\n", suite);

Post by Kevin Long
Hi folks,
At least several endpoints (soft phone and desk phones) are supporting various 256 bit ciphers for SRTP these days. I *believe* libsrtp has been updated to allow this, and that only the code in Asterisk has not been been updated to allow these stronger ciphers.
Would anyone with the know-how be willing/able to submit a patch ?
Thank you,
Kevin Long
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[Joshua Colp]

Post by Kevin Long
Some more information (would love some thoughts on this, I have never
submitted a patch yet).
AES_CM_128_HMAC_SHA1_32 AES_CM_128_HMAC_SHA1_80
AES_CM_192_HMAC_SHA1_32 AES_CM_192_HMAC_SHA1_80
AES_CM_256_HMAC_SHA1_32 AES_CM_256_HMAC_SHA1_80 AEAD_AES_128_GCM
AEAD_AES_256_GCM
Could adding support for the above cipher suites be as simple as
adding more options to this switch/case statement with the
appropriate parameters or is there more to it?
Thank you!
static int policy_set_suite(crypto_policy_t *p, enum ast_srtp_suite
p->cipher_type = AES_128_ICM; p->cipher_key_len = 30; p->auth_type =
HMAC_SHA1; p->auth_key_len = 20; p->auth_tag_len = 10; p->sec_serv =
sec_serv_conf_and_auth; return 0;
case AST_AES_CM_128_HMAC_SHA1_32: p->cipher_type = AES_128_ICM;
p->cipher_key_len = 30; p->auth_type = HMAC_SHA1; p->auth_key_len =
20; p->auth_tag_len = 4; p->sec_serv = sec_serv_conf_and_auth; return
0;
default: ast_log(LOG_ERROR, "Invalid crypto suite: %u\n", suite);

It could maybe be as simple as that, but until it is attempted it's
unknown what other stuff may need to be adjusted.

Cheers,
--
Joshua Colp
Digium, Inc. | Senior Software Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - US
Check us out at: www.digium.com & www.asterisk.org