- markus@cvs.openbsd.org 2002/08/02 22:20:30

     [ssh-rsa.c]
     replace RSA_verify with our own version and avoid the OpenSSL ASN.1 parser
     for authentication; ok deraadt/djm

1 files changed, 93 insertions, 7 deletions

diff --git a/ssh-rsa.c b/ssh-rsa.c
index 8271af42b..44287fa26 100644
--- a/ssh-rsa.c
+++ b/ssh-rsa.c
@@ -23,7 +23,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: ssh-rsa.c,v 1.24 2002/08/02 21:23:41 markus Exp $");
+RCSID("$OpenBSD: ssh-rsa.c,v 1.25 2002/08/02 22:20:30 markus Exp $");
 
 #include <openssl/evp.h>
 #include <openssl/err.h>
@@ -37,6 +37,8 @@ RCSID("$OpenBSD: ssh-rsa.c,v 1.24 2002/08/02 21:23:41 markus Exp $");
 #include "compat.h"
 #include "ssh.h"
 
+static int openssh_RSA_verify(int, u_char *, u_int, u_char *, u_int , RSA *);
+
 /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
 int
 ssh_rsa_sign(Key *key, u_char **sigp, u_int *lenp,
@@ -167,15 +169,99 @@ ssh_rsa_verify(Key *key, u_char *signature, u_int signaturelen,
         EVP_DigestUpdate(&md, data, datalen);
         EVP_DigestFinal(&md, digest, &dlen);
 
-        ret = RSA_verify(nid, digest, dlen, sigblob, len, key->rsa);
+        ret = openssh_RSA_verify(nid, digest, dlen, sigblob, len, key->rsa);
         memset(digest, 'd', sizeof(digest));
         memset(sigblob, 's', len);
         xfree(sigblob);
-        if (ret == 0) {
-                int ecode = ERR_get_error();
-                error("ssh_rsa_verify: RSA_verify failed: %s",
-                    ERR_error_string(ecode, NULL));
-        }
         debug("ssh_rsa_verify: signature %scorrect", (ret==0) ? "in" : "");
         return ret;
 }
+
+/*
+ * See:
+ * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
+ * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
+ */
+/*
+ * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
+ *      oiw(14) secsig(3) algorithms(2) 26 }
+ */
+static const u_char id_sha1[] = {
+        0x30, 0x21, /* type Sequence, length 0x21 (33) */
+        0x30, 0x09, /* type Sequence, length 0x09 */
+        0x06, 0x05, /* type OID, length 0x05 */
+        0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
+        0x05, 0x00, /* NULL */
+        0x04, 0x14  /* Octet string, length 0x14 (20), followed by sha1 hash */
+};
+/*
+ * id-md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
+ *      rsadsi(113549) digestAlgorithm(2) 5 }
+ */
+static const u_char id_md5[] = {
+        0x30, 0x20, /* type Sequence, length 0x20 (32) */
+        0x30, 0x0c, /* type Sequence, length 0x09 */
+        0x06, 0x08, /* type OID, length 0x05 */
+        0x2a, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* id-md5 */
+        0x05, 0x00, /* NULL */
+        0x04, 0x10  /* Octet string, length 0x10 (16), followed by md5 hash */
+};
+
+static int
+openssh_RSA_verify(int type, u_char *hash, u_int hashlen,
+    u_char *sigbuf, u_int siglen, RSA *rsa)
+{
+        u_int ret, rsasize, len, oidlen = 0, hlen = 0;
+        const u_char *oid = NULL;
+        u_char *decrypted = NULL;
+
+        ret = 0;
+        switch (type) {
+        case NID_sha1:
+                oid = id_sha1;
+                oidlen = sizeof(id_sha1);
+                hlen = 20;
+                break;
+        case NID_md5:
+                oid = id_md5;
+                oidlen = sizeof(id_md5);
+                hlen = 16;
+                break;
+        default:
+                goto done;
+                break;
+        }
+        if (hashlen != hlen) {
+                error("bad hashlen");
+                goto done;
+        }
+        rsasize = RSA_size(rsa);
+        if (siglen == 0 || siglen > rsasize) {
+                error("bad siglen");
+                goto done;
+        }
+        decrypted = xmalloc(rsasize);
+        if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
+            RSA_PKCS1_PADDING)) < 0) {
+                error("RSA_public_decrypt failed: %s",
+                    ERR_error_string(ERR_get_error(), NULL));
+                goto done;
+        }
+        if (len != hlen + oidlen) {
+                error("bad decrypted len: %d != %d + %d", len, hlen, oidlen);
+                goto done;
+        }
+        if (memcmp(decrypted, oid, oidlen) != 0) {
+                error("oid mismatch");
+                goto done;
+        }
+        if (memcmp(decrypted + oidlen, hash, hlen) != 0) {
+                error("hash mismatch");
+                goto done;
+        }
+        ret = 1;
+done:
+        if (decrypted)
+                xfree(decrypted);
+        return ret;
+}