On 16 aug 2012, at 20:20, Wayne Blacklock wrote:
When everything isn't ok, the SSL decryption fails:
ssl_decrypt_pre_master_secret:RSA_private_decrypt
pcry_private_decrypt: stripping 146 bytes, decr_len 255
decrypted_unstrip_pre_master[255]:
<snip>
ssl_decrypt_pre_master_secret wrong pre_master_secret length (109, expected 48)
dissect_ssl3_handshake can't decrypt pre master secret
Now I am
no SSL expert, but I don't think this is right. What I hope to
understand and the reason for this post, is how exactly the byte
stripping works... where does the SSL decrypter get 146 from and could
this explain our SSL issues? If so, what exactly is going wrong? I've
had a bit of a look through the TLS spec but it isn't clear to me and so
I would appreciate any and all advice.
The only situations where I have seen the message "wrong pre_master_secret length" were when the public key in the server certificate did not match the provided private key. Can you verify that the *exact* same certificate is used in both sessions?
/* strip the padding*/
rc = 0;
for (i = 1; i < decr_len; i++) {
if (decr_data_ptr[i] == 0) {
rc = i+1;
break;
}
}
ssl_debug_printf("pcry_private_decrypt: stripping %d bytes, decr_len %d\n",
rc, decr_len);
ssl_print_data("decrypted_unstrip_pre_master", decr_data_ptr, decr_len);
g_memmove(decr_data_ptr, &decr_data_ptr[rc], decr_len - rc);
In other words, the decrypted (unstripped) PreMasterSecret is searched for the first occurrence of the value 0. Everything after the first 0 is then used as the PreMasterSecret and it should be exactly 48 bytes long.
pre master encrypted[128]:
76 1b 1b ea c3 5e 59 de 9a 3b b9 f7 4e bf 91 09
b7 38 e8 ad 34 6c 3c e8 26 f8 e9 f6 5d 82 a9 a5
44 c6 0a fe ae 85 6d 01 1f 5d 11 4d 1f 16 d2 4a
64 13 ad 32 c2 92 1d 54 b8 f2 6b d2 bb a5 7b 55
73 87 69 ff 33 bb 9f aa 57 27 3a 58 43 61 29 46
c2 12 6d f3 6d c8 98 4b df 72 7a 7c 67 72 89 5d
c5 3d 5d 8f c5 d8 43 68 86 f6 70 f0 d9 b7 91 36
1c 8a a4 bd 64 b0 27 d4 c0 2d 03 dd 92 f7 df 36
ssl_decrypt_pre_master_secret:RSA_private_decrypt
pcry_private_decrypt: stripping 79 bytes, decr_len 127
decrypted_unstrip_pre_master[127]:
02 54 f5 61 13 68 03 30 97 14 1f e9 cc 7c 2c 3b
d2 b0 f6 db 18 f7 2b 81 e0 46 ad 51 dd 26 b3 fe
94 48 ab 8a 52 db 97 e3 df 9e e4 30 64 96 3e d1
b4 9a 13 8f e4 ad c0 1d 98 10 e8 dc 0d 89 02 85
5c 03 3b 5b 9e 71 51 3a df 30 20 40 be 9e 00 03
01 90 36 b9 c6 b5 f1 2d 7d 3b 6b 3c bb 6a 7c ed
9a 4c 38 1e 07 67 c6 07 fb 51 5a 0c 2e 2b 3b 41
96 5a 6f fc d2 88 86 59 ff aa 82 7f e5 bb 42
pre master secret[48]:
03 01 90 36 b9 c6 b5 f1 2d 7d 3b 6b 3c bb 6a 7c
ed 9a 4c 38 1e 07 67 c6 07 fb 51 5a 0c 2e 2b 3b
41 96 5a 6f fc d2 88 86 59 ff aa 82 7f e5 bb 42
