CODEWITHSUNDEEP
sslencryptionopensslpyopenssl
Hassan Anwer
Hassan Anwer

Reputation: 367

Find SSL Version after Handshake in OpenSSL

I want to find out the protocols supported by a target but the problem is that their are quite a number websites which are not supporting a particular version but when i performed handshake it was successful becz target surpassed the version that i gave and perform handshake on the supported version [ it happened on only 1 website]

example : i passed a version :TLSVersion.TLS_1_2 but the handshake is performed using TLSv1_0 becz it is not supporting TLSVersion.TLS_1_2

Because of the above issue i want to check the version on handshake and i dont want to use scapy.ssl_tls

version = [SSL.SSLv23_METHOD,
            SSL.TLSv1_METHOD,
            SSL.TLSv1_1_METHOD,
            SSL.TLSv1_2_METHOD]
context = OpenSSL.SSL.Context(version)
soc = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
soc.settimeout(CONNECTION_TIMEOUT)
connection = OpenSSL.SSL.Connection(context,soc)
connection.connect((host,port))
connection.do_handshake() 
#wants to check version here

Upvotes: 3

Views: 4568

Answers (2)

Steffen Ullrich
Steffen Ullrich

Reputation: 123320

i want to check the version on handshake

The relevant functions to check the version both client and server use for the remaining session in pyOpenSSL are get_protocol_version_name or get_protocol_version:

connection.do_handshake()
#wants to check version here
print(connection.get_protocol_version_name())

Note that these functions are only available since pyOpenSSL 0.16.0

Please not also that you cannot specify a list of TLS methods when creating the context but only a single method which essentially specifies the minimal TLS version supported by the client. Thus

context = OpenSSL.SSL.Context(SSL.TLSv1_METHOD)

allows the client to use TLS 1.0 and better. If you instead use SSL.TLSv1_2_METHOD the client would be restricted to TLS 1.2 and better and thus could not establish a SSL connection with a server supporting only TLS 1.0.

Upvotes: 3

jww
jww

Reputation: 102246

Find SSL Version after Handshake in OpenSSL...

If I am parsing what you want correctly... you want the protocol version like printed by openssl s_client:

$ openssl version
OpenSSL 1.1.0b  26 Sep 2016

$ openssl s_client -connect www.google.com:443 -servername www.google.com
CONNECTED(00000005)
depth=2 C = US, O = GeoTrust Inc., CN = GeoTrust Global CA
verify error:num=20:unable to get local issuer certificate
Server did acknowledge servername extension.
---
...
---
New, TLSv1.2, Cipher is ECDHE-RSA-CHACHA20-POLY1305
Server public key is 2048 bit
Secure Renegotiation IS supported
No ALPN negotiated
SSL-Session:
    Protocol  : TLSv1.2
...

The first message of "New, TLSv1.2" tells you about the cipher. That is, when is ECDHE-RSA-CHACHA20-POLY1305 first arrived in TLS. In the case of ECDHE-RSA-CHACHA20-POLY1305, the cipher suite was first seen in TLS 1.2.

The source code for s_client is located at <openssl src>/apps/s_client.c. The code responsible in OpenSSL 1.0.2 is around line 2210:

/* line 2210 */
c = SSL_get_current_cipher(s);
BIO_printf(bio, "%s, Cipher is %s\n",
           SSL_CIPHER_get_version(c), SSL_CIPHER_get_name(c));
...

The second message of "Protocol: TLSv1.2" tells you the protocol version used during key exchange and subsequent cipher selection and bulk transfer.

The code responsible in OpenSSL 1.0.2 is <openssl src>/ssl/ssl_txt.c around line 105:

/* line 105 */
int SSL_SESSION_print(BIO *bp, const SSL_SESSION *x)
{
    unsigned int i;
    const char *s;

    if (x == NULL)
        goto err;
    if (BIO_puts(bp, "SSL-Session:\n") <= 0)
        goto err;
    if (x->ssl_version == SSL2_VERSION)
        s = "SSLv2";
    else if (x->ssl_version == SSL3_VERSION)
        s = "SSLv3";
    else if (x->ssl_version == TLS1_2_VERSION)
        s = "TLSv1.2";
    else if (x->ssl_version == TLS1_1_VERSION)
        s = "TLSv1.1";
    else if (x->ssl_version == TLS1_VERSION)
        s = "TLSv1";
    else if (x->ssl_version == DTLS1_VERSION)
        s = "DTLSv1";
    else if (x->ssl_version == DTLS1_2_VERSION)
        s = "DTLSv1.2";
    else if (x->ssl_version == DTLS1_BAD_VER)
        s = "DTLSv1-bad";
    else
        s = "unknown";
    if (BIO_printf(bp, "    Protocol  : %s\n", s) <= 0)
        goto err;

    ...
}

I want to find out the protocols supported by a target but the problem is that their are quite a number websites which are not supporting a particular version but when i performed handshake ...

This is a different problem. You should look at the source code for sslscan at SSLScan - Fast SSL Scanner to see how it works. The Sourceforge one seems abandoned. It lacks SNI and other new features, like secure negotiation and ALPN.

You might try this sslscan from GitHub: rbsec/sslscan. The GitHub one is actively maintained and seems to be more up to date.

example : i passed a version :TLSVersion.TLS_1_2 but the handshake is performed using TLSv1_0 becz it is not supporting TLSVersion.TLS_1_2

This will not happen. TLS specifies one protocol version only. The idea is your try TLS 1.2. If it fails, then you fall back to TLS 1.1. If it fails, then you fall back to TLS 1.0. Ad infinitum.

The try-and-fallback approach is the reason for RFC 7504, TLS Fallback Signaling Cipher Suite Value (SCSV) for Preventing Protocol Downgrade Attacks. This was an awful band-aide from the Browser crowd. See, for example, Last Call: <draft-ietf-tls-downgrade-scsv-03.txt> (TLS Fallback Signaling Cipher Suite Value (SCSV) for Preventing Protocol Downgrade Attacks) to Proposed Standard.

TLS does not accept a range of protocol versions like many folks think. We have tried to get it changed a few times. See, for example, A new TLS version negotiation mechanism.

Upvotes: 3

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