SSL keylogging for libssl.35.dylib for MobileDevice.framework

libressllog.js

// This script implements SSL keylogging for libssl.35.dylib, which is an old version of LibreSSL.
// Primarily intended to be used when debugging MobileDevice.framework, which uses it for some reason.

var mod = Process.getModuleByName("libssl.35.dylib");
var gen_master = mod.findExportByName("tls1_generate_master_secret");

var keylogPath = '/tmp/keylog.txt';
var keylog = new File(keylogPath, "a");

var toHex = function(arr) {
    return Array.from(new Uint8Array(arr))
        .map(b => b.toString(16).padStart(2, '0')).join('');
};

Interceptor.attach(gen_master, {
    onEnter(args) {
        this.ssl = args[0];
        this.master_key_buf = args[1];
    },
    onLeave(r) {
        try {
            var master_key_len = r.toInt32();
            if (master_key_len <= 0) return;

            var master_key = this.master_key_buf.readByteArray(master_key_len);

/*
From LibreSSL 2.2.9:

struct ssl_st {
    int version;                    // 0x00  4 bytes
    int type;                       // 0x04  4 bytes
    const SSL_METHOD *method;       // 0x08  8 bytes
    BIO *rbio;                      // 0x10  8 bytes
    BIO *wbio;                      // 0x18  8 bytes
    BIO *bbio;                      // 0x20  8 bytes
    int rwstate;                    // 0x28  4 bytes
    int in_handshake;               // 0x2c  4 bytes
    int (*handshake_func)(SSL *);   // 0x30  8 bytes
    int server;                     // 0x38  4 bytes
    int new_session;                // 0x3c  4 bytes
    int quiet_shutdown;             // 0x40  4 bytes
    int shutdown;                   // 0x44  4 bytes
    int state;                      // 0x48  4 bytes
    int rstate;                     // 0x4c  4 bytes
    BUF_MEM *init_buf;              // 0x50  8 bytes
    void *init_msg;                 // 0x58  8 bytes
    int init_num;                   // 0x60  4 bytes
    int init_off;                   // 0x64  4 bytes
    unsigned char *packet;          // 0x68  8 bytes
    unsigned int packet_length;     // 0x70  4 bytes
    // 4 bytes padding
    struct ssl3_state_st *s3;       // 0x78  8 bytes  <---
}; 

typedef struct ssl3_state_st {
    long flags;                                     // 0x00   8 bytes
    int delay_buf_pop_ret;                          // 0x08   4 bytes
    unsigned char read_sequence[8];                 // 0x0c   8 bytes
    int read_mac_secret_size;                       // 0x14   4 bytes
    unsigned char read_mac_secret[64];              // 0x18  64 bytes
    unsigned char write_sequence[8];                // 0x58   8 bytes
    int write_mac_secret_size;                      // 0x60   4 bytes
    unsigned char write_mac_secret[64];             // 0x64  64 bytes
    unsigned char server_random[32];                // 0xa4  32 bytes
    unsigned char client_random[32];                // 0xc4  32 bytes  <---
};
*/
            var s3 = this.ssl.add(0x78).readPointer();
            var client_random = s3.add(0xC4).readByteArray(32);

            var line = "CLIENT_RANDOM " + toHex(client_random) + " " + toHex(master_key) + "\n";
            keylog.write(line);
            keylog.flush();
            console.log(line.trim());
        } catch(e) {
            console.log("Error: " + e);
        }
    }
});

console.log("TLS keylog active, writing to: " + keylogPath);