X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=blobdiff_plain;f=crypt_common.c;h=277897f2b47a3c9587d4bb08a5b634b7d4c53f46;hp=08361b27104d6a4658e151259ba6f0ae585205c0;hb=74f74cde7afdba9cfe316998aba9286764bb5d34;hpb=767a4a54c967bc4b80bd14d02e89fe91acd848dd

diff --git a/crypt_common.c b/crypt_common.c
index 08361b27..277897f2 100644
--- a/crypt_common.c
+++ b/crypt_common.c
@@ -10,20 +10,19 @@
 #include "crypt.h"
 #include "crypt_backend.h"
 #include "portable_io.h"
+#include "fd.h"
+#include "base64.h"
 
 /** If the key begins with this text, we treat it as an ssh key. */
 #define KEY_TYPE_TXT "ssh-rsa"
 
-/**
- * Check if given buffer starts with a ssh rsa key signature.
- *
- * \param data The buffer.
- * \param size Number of data bytes.
+/*
+ * Check if the given buffer starts with an ssh rsa key signature.
  *
- * \return Number of header bytes to be skipped on success, zero if
- * ssh rsa signature was not found.
+ * Returns number of header bytes to be skipped on success, zero if no ssh rsa
+ * signature was found.
  */
-size_t is_ssh_rsa_key(char *data, size_t size)
+static size_t is_ssh_rsa_key(char *data, size_t size)
 {
 	char *cp;
 
@@ -42,20 +41,13 @@ size_t is_ssh_rsa_key(char *data, size_t size)
 	return cp - data;
 }
 
-/**
- * Sanity checks for the header of an ssh key.
- *
- * \param blob The buffer.
- * \param blen The number of bytes of \a blob.
+/*
+ * Perform some sanity checks on the decoded ssh key.
  *
- * This performs some checks to make sure we really have an ssh key. It also
- * computes the offset in bytes of the start of the key values (modulus,
- * exponent..).
- *
- * \return The number of bytes to skip until the start of the first encoded
- * number (usually 11).
+ * This function returns the size of the header. Usually, the header is 11
+ * bytes long: four bytes for the length field, and the string "ssh-rsa".
  */
-int check_ssh_key_header(const unsigned char *blob, int blen)
+static int check_ssh_key_header(const unsigned char *blob, int blen)
 {
 	const unsigned char *p = blob, *end = blob + blen;
 	uint32_t rlen;
@@ -76,6 +68,51 @@ int check_ssh_key_header(const unsigned char *blob, int blen)
 	return 4 + rlen;
 }
 
+/**
+ * Perform sanity checks and base64-decode an ssh-rsa key.
+ *
+ * \param filename The public key file (usually id_rsa.pub).
+ * \param blob Pointer to base64-decoded blob is returned here.
+ * \param decoded_size The size of the decoded blob.
+ *
+ * The memory pointed at by the returned blob pointer has to be freed by the
+ * caller.
+ *
+ * \return On success, the offset in bytes of the start of the key values
+ * (modulus, exponent..). This is the number of bytes to skip from the blob
+ * until the start of the first encoded number. On failure, a negative error
+ * code is returned.
+ *
+ * \sa \ref uudecode().
+ */
+int decode_public_key(const char *filename, unsigned char **blob,
+		size_t *decoded_size)
+{
+	int ret, ret2;
+	void *map;
+	size_t map_size;
+
+	ret = mmap_full_file(filename, O_RDONLY, &map, &map_size, NULL);
+	if (ret < 0)
+		return ret;
+	ret = is_ssh_rsa_key(map, map_size);
+	if (ret == 0) {
+		ret = -E_SSH_PARSE;
+		goto unmap;
+	}
+	ret = uudecode(map + ret, map_size - ret, (char **)blob, decoded_size);
+	if (ret < 0)
+		goto unmap;
+	ret = check_ssh_key_header(*blob, *decoded_size);
+	if (ret < 0)
+		goto unmap;
+unmap:
+	ret2 = para_munmap(map, map_size);
+	if (ret >= 0 && ret2 < 0)
+		ret = ret2;
+	return ret;
+}
+
 /**
  * Check existence and permissions of a private key file.
  *
@@ -122,3 +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;
+}
+