gcrypt: Add support for RFC4716 private keys.
[paraslash.git] / crypt_common.c
index 2b2e06c..277897f 100644 (file)
@@ -159,3 +159,74 @@ int hash_compare(unsigned char *h1, unsigned char *h2)
        }
        return 0;
 }
+
+/**
+ * Check header of an openssh private key and compute bignum offset.
+ *
+ * \param data The base64-decoded key.
+ * \param len The size of the decoded key.
+ *
+ * Several assumptions are made about the key. Most notably, we only support
+ * single unencrypted keys without comments.
+ *
+ * \return The offset at which the first bignum of the private key (the public
+ * exponent n) starts. Negative error code on failure.
+ */
+int find_openssh_bignum_offset(const unsigned char *data, int len)
+{
+       /*
+        * Unencrypted keys without comments always start with the below byte
+        * sequence. See PROTOCOL.key of the openssh package.
+        */
+       static const unsigned char valid_openssh_header[] = {
+               /* string "openssh-key-v1" */
+               0x6f, 0x70, 0x65, 0x6e, 0x73, 0x73, 0x68, 0x2d, 0x6b, 0x65,
+                       0x79, 0x2d, 0x76, 0x31,
+               /* length of the cipher name */
+               0x00, 0x00, 0x00, 0x00, 0x04,
+               /* cipher name: "none" */
+               0x6e, 0x6f, 0x6e, 0x65,
+               /* length of the kdfname (only used for encrypted keys) */
+               0x00, 0x00, 0x00, 0x04,
+               /* kdfname: "none" */
+               0x6e, 0x6f, 0x6e, 0x65,
+               /* length of kdfoptions */
+               0x00, 0x00, 0x00, 0x00,
+               /* number of keys */
+               0x00, 0x00, 0x00, 0x01,
+       };
+       uint32_t val;
+       const unsigned char *p, *end = data + len;
+
+       if (len <= sizeof(valid_openssh_header) + 4)
+               return -E_OPENSSH_PARSE;
+       if (memcmp(data, valid_openssh_header, sizeof(valid_openssh_header)))
+               return -E_OPENSSH_PARSE;
+       p = data + sizeof(valid_openssh_header);
+       /* length of public key */
+       val = read_u32_be(p);
+       if (val > end - p - 4)
+               return -E_OPENSSH_PARSE;
+       p += val + 4;
+       /* length of private key */
+       val = read_u32_be(p);
+       if (val > end - p - 4)
+               return -E_OPENSSH_PARSE;
+       p += 4;
+       /* two equal random integers ("checkint") */
+       if (p + 8 > end)
+               return -E_OPENSSH_PARSE;
+       if (read_u32_be(p) != read_u32_be(p + 4))
+               return -E_OPENSSH_PARSE;
+       p += 8;
+       /* length of name of key type "ssh-rsa" */
+       if (p + 11 > end)
+               return -E_OPENSSH_PARSE;
+       if (read_u32_be(p) != 7)
+               return -E_OPENSSH_PARSE;
+       if (memcmp(p + 4, "ssh-rsa", 7))
+               return -E_OPENSSH_PARSE;
+       p += 11;
+       return p - data;
+}
+