diff --git a/signature.c b/signature.c
new file mode 100644
index 0000000..b2a7084
--- /dev/null
+++ b/signature.c
@@ -0,0 +1,161 @@
+/* 
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that: (1) source code
+ * distributions retain the above copyright notice and this paragraph
+ * in its entirety, and (2) distributions including binary code include
+ * the above copyright notice and this paragraph in its entirety in
+ * the documentation or other materials provided with the distribution.
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND
+ * WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT
+ * LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE.
+ *
+ * Functions for signature and digest verification.
+ * 
+ * Original code by Hannes Gredler (hannes@juniper.net)
+ */
+
+#ifndef lint
+static const char rcsid[] _U_ =
+    "@(#) $Header: /tcpdump/master/tcpdump/signature.c,v 1.2 2008-09-22 20:22:10 guy Exp $ (LBL)";
+#endif
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <tcpdump-stdinc.h>
+
+#include <string.h>
+
+#include "interface.h"
+#include "signature.h"
+
+#ifdef HAVE_LIBCRYPTO
+#include <openssl/md5.h>
+#endif
+
+const struct tok signature_check_values[] = {
+    { SIGNATURE_VALID, "valid"},
+    { SIGNATURE_INVALID, "invalid"},
+    { CANT_CHECK_SIGNATURE, "unchecked"},
+    { 0, NULL }
+};
+
+
+#ifdef HAVE_LIBCRYPTO
+/*
+ * Compute a HMAC MD5 sum.
+ * Taken from rfc2104, Appendix.
+ */
+USES_APPLE_DEPRECATED_API
+static void
+signature_compute_hmac_md5(const u_int8_t *text, int text_len, unsigned char *key,
+                           unsigned int key_len, u_int8_t *digest)
+{
+    MD5_CTX context;
+    unsigned char k_ipad[65];    /* inner padding - key XORd with ipad */
+    unsigned char k_opad[65];    /* outer padding - key XORd with opad */
+    unsigned char tk[16];
+    int i;
+
+    /* if key is longer than 64 bytes reset it to key=MD5(key) */
+    if (key_len > 64) {
+
+        MD5_CTX tctx;
+
+        MD5_Init(&tctx);
+        MD5_Update(&tctx, key, key_len);
+        MD5_Final(tk, &tctx);
+
+        key = tk;
+        key_len = 16;
+    }
+
+    /*
+     * the HMAC_MD5 transform looks like:
+     *
+     * MD5(K XOR opad, MD5(K XOR ipad, text))
+     *
+     * where K is an n byte key
+     * ipad is the byte 0x36 repeated 64 times
+     * opad is the byte 0x5c repeated 64 times
+     * and text is the data being protected
+     */
+
+    /* start out by storing key in pads */
+    memset(k_ipad, 0, sizeof k_ipad);
+    memset(k_opad, 0, sizeof k_opad);
+    memcpy(k_ipad, key, key_len);
+    memcpy(k_opad, key, key_len);
+
+    /* XOR key with ipad and opad values */
+    for (i=0; i<64; i++) {
+        k_ipad[i] ^= 0x36;
+        k_opad[i] ^= 0x5c;
+    }
+
+    /*
+     * perform inner MD5
+     */
+    MD5_Init(&context);                   /* init context for 1st pass */
+    MD5_Update(&context, k_ipad, 64);     /* start with inner pad */
+    MD5_Update(&context, text, text_len); /* then text of datagram */
+    MD5_Final(digest, &context);          /* finish up 1st pass */
+
+    /*
+     * perform outer MD5
+     */
+    MD5_Init(&context);                   /* init context for 2nd pass */
+    MD5_Update(&context, k_opad, 64);     /* start with outer pad */
+    MD5_Update(&context, digest, 16);     /* then results of 1st hash */
+    MD5_Final(digest, &context);          /* finish up 2nd pass */
+}
+USES_APPLE_RST
+#endif
+
+#ifdef HAVE_LIBCRYPTO
+/*
+ * Verify a cryptographic signature of the packet.
+ * Currently only MD5 is supported.
+ */
+int
+signature_verify (const u_char *pptr, u_int plen, u_char *sig_ptr)
+{
+    u_int8_t rcvsig[16];
+    u_int8_t sig[16];
+    unsigned int i;
+
+    /*
+     * Save the signature before clearing it.
+     */
+    memcpy(rcvsig, sig_ptr, sizeof(rcvsig));
+    memset(sig_ptr, 0, sizeof(rcvsig));
+
+    if (!sigsecret) {
+        return (CANT_CHECK_SIGNATURE);
+    }
+
+    signature_compute_hmac_md5(pptr, plen, (unsigned char *)sigsecret,
+                               strlen(sigsecret), sig);
+
+    if (memcmp(rcvsig, sig, sizeof(sig)) == 0) {
+        return (SIGNATURE_VALID);
+
+    } else {
+
+        for (i = 0; i < sizeof(sig); ++i) {
+            (void)printf("%02x", sig[i]);
+        }
+
+        return (SIGNATURE_INVALID);
+    }
+}
+#endif
+
+/*
+ * Local Variables:
+ * c-style: whitesmith
+ * c-basic-offset: 4
+ * End:
+ */