X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=blobdiff_plain;f=crypt_common.c;h=277897f2b47a3c9587d4bb08a5b634b7d4c53f46;hp=2b2e06c169c64064db47c850e03c81cd309f6b8c;hb=74f74cde7afdba9cfe316998aba9286764bb5d34;hpb=3e0533843c8d4add881a6c2d383bd2c80129e27b

diff --git a/crypt_common.c b/crypt_common.c
index 2b2e06c1..277897f2 100644
--- a/crypt_common.c
+++ b/crypt_common.c
@@ -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;
+}
+