From f5f31a868db4fc79a430ce264a7c13660f23fbe5 Mon Sep 17 00:00:00 2001
From: Peter Wu <peter@lekensteyn.nl>
Date: Wed, 28 Jan 2015 19:49:22 +0100
Subject: sslkeylog.c: utility to intercept OpenSSL keys

For a gdb function, see http://security.stackexchange.com/a/80174/2630
To generate the line assuming you have a context with a SSL structure
(named "s") run this:

    python
    def read_as_hex(name, size):
        addr = gdb.parse_and_eval(name).address
        data = gdb.selected_inferior().read_memory(addr, size)
        return ''.join('%02X' % ord(x) for x in data)

    def pm(ssl='s'):
        mk = read_as_hex('%s->session->master_key' % ssl, 48)
        cr = read_as_hex('%s->s3->client_random' % ssl, 32)
        print('CLIENT_RANDOM %s %s' % (cr, mk))
    end
    python pm()
---
 src/sslkeylog.c | 88 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 src/sslkeylog.c

(limited to 'src/sslkeylog.c')

diff --git a/src/sslkeylog.c b/src/sslkeylog.c
new file mode 100644
index 0000000..ade40cb
--- /dev/null
+++ b/src/sslkeylog.c
@@ -0,0 +1,88 @@
+/*
+ * Dumps master keys for OpenSSL clients to file. The format is documented at
+ * https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/Key_Log_Format
+ *
+ * Copyright (C) 2014 Peter Wu <peter@lekensteyn.nl>
+ * Licensed under the terms of GPLv3 (or any later version) at your choice.
+ *
+ * Usage:
+ *  cc sslkeylog.c -shared -o libsslkeylog.so -fPIC -ldl
+ *  SSLKEYLOGFILE=premaster.txt LD_PRELOAD=./libsslkeylog.so openssl ...
+ */
+#define _GNU_SOURCE /* for RTLD_NEXT */
+#include <dlfcn.h>
+#include <openssl/ssl.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+
+#define PREFIX      "CLIENT_RANDOM "
+#define PREFIX_LEN  (sizeof(PREFIX) - 1)
+#define FIRSTLINE   "# SSL key logfile generated by sslkeylog.c\n"
+#define FIRSTLINE_LEN (sizeof(FIRSTLINE) - 1)
+
+static int (*_SSL_connect)(SSL *ssl);
+static int key_logfile_fd = -1;
+
+static inline void put_hex(char *buffer, int pos, char c)
+{
+    unsigned char c1 = ((unsigned char) c) >> 4;
+    unsigned char c2 = c & 0xF;
+    buffer[pos] = c1 < 10 ? '0' + c1 : 'A' + c1 - 10;
+    buffer[pos+1] = c2 < 10 ? '0' + c2 : 'A' + c2 - 10;
+}
+
+static void dump_to_fd(SSL *ssl, int fd)
+{
+    int pos, i;
+    char line[PREFIX_LEN + 2 * SSL3_RANDOM_SIZE + 1 +
+              2 * SSL_MAX_MASTER_KEY_LENGTH + 1];
+
+    memcpy(line, PREFIX, PREFIX_LEN);
+    pos = PREFIX_LEN;
+    /* Client Random for SSLv3/TLS */
+    for (i = 0; i < SSL3_RANDOM_SIZE; i++) {
+        put_hex(line, pos, ssl->s3->client_random[i]);
+        pos += 2;
+    }
+    line[pos++] = ' ';
+    /* Master Secret (size is at most SSL_MAX_MASTER_KEY_LENGTH) */
+    for (i = 0; i < ssl->session->master_key_length; i++) {
+        put_hex(line, pos, ssl->session->master_key[i]);
+        pos += 2;
+    }
+    line[pos++] = '\n';
+    /* Write at once rather than using buffered I/O. Perhaps there is concurrent
+     * write access so do not write hex values one by one. */
+    write(fd, line, pos);
+}
+
+static void init_key_logfile(void)
+{
+    if (key_logfile_fd >= 0)
+        return;
+
+    const char *filename = getenv("SSLKEYLOGFILE");
+    if (filename) {
+        key_logfile_fd = open(filename, O_WRONLY | O_APPEND | O_CREAT, 0644);
+        if (key_logfile_fd >= 0 && lseek(key_logfile_fd, 0, SEEK_END) == 0) {
+            /* file is opened successfully and there is no data (pos == 0) */
+            write(key_logfile_fd, FIRSTLINE, FIRSTLINE_LEN);
+        }
+    }
+}
+
+int SSL_connect(SSL *ssl)
+{
+    if (!_SSL_connect) {
+        _SSL_connect = (int (*)(SSL *ssl)) dlsym(RTLD_NEXT, "SSL_connect");
+    }
+    int ret = _SSL_connect(ssl);
+    if (ret >= 0) {
+        init_key_logfile();
+        if (key_logfile_fd >= 0) {
+            dump_to_fd(ssl, key_logfile_fd);
+        }
+    }
+    return ret;
+}
-- 
cgit v1.2.1