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-rw-r--r--agent/pksign.c572
1 files changed, 572 insertions, 0 deletions
diff --git a/agent/pksign.c b/agent/pksign.c
new file mode 100644
index 0000000..09d61b8
--- /dev/null
+++ b/agent/pksign.c
@@ -0,0 +1,572 @@
+/* pksign.c - public key signing (well, actually using a secret key)
+ * Copyright (C) 2001-2004, 2010 Free Software Foundation, Inc.
+ * Copyright (C) 2001-2004, 2010, 2013 Werner Koch
+ *
+ * This file is part of GnuPG.
+ *
+ * GnuPG is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * GnuPG is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <config.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
+#include <assert.h>
+#include <unistd.h>
+#include <sys/stat.h>
+
+#include "agent.h"
+#include "../common/i18n.h"
+
+
+static int
+do_encode_md (const byte * md, size_t mdlen, int algo, gcry_sexp_t * r_hash,
+ int raw_value)
+{
+ gcry_sexp_t hash;
+ int rc;
+
+ if (!raw_value)
+ {
+ const char *s;
+ char tmp[16+1];
+ int i;
+
+ s = gcry_md_algo_name (algo);
+ if (s && strlen (s) < 16)
+ {
+ for (i=0; i < strlen (s); i++)
+ tmp[i] = tolower (s[i]);
+ tmp[i] = '\0';
+ }
+
+ rc = gcry_sexp_build (&hash, NULL,
+ "(data (flags pkcs1) (hash %s %b))",
+ tmp, (int)mdlen, md);
+ }
+ else
+ {
+ gcry_mpi_t mpi;
+
+ rc = gcry_mpi_scan (&mpi, GCRYMPI_FMT_USG, md, mdlen, NULL);
+ if (!rc)
+ {
+ rc = gcry_sexp_build (&hash, NULL,
+ "(data (flags raw) (value %m))",
+ mpi);
+ gcry_mpi_release (mpi);
+ }
+ else
+ hash = NULL;
+
+ }
+
+ *r_hash = hash;
+ return rc;
+}
+
+
+/* Return the number of bits of the Q parameter from the DSA key
+ KEY. */
+static unsigned int
+get_dsa_qbits (gcry_sexp_t key)
+{
+ gcry_sexp_t l1, l2;
+ gcry_mpi_t q;
+ unsigned int nbits;
+
+ l1 = gcry_sexp_find_token (key, "private-key", 0);
+ if (!l1)
+ l1 = gcry_sexp_find_token (key, "protected-private-key", 0);
+ if (!l1)
+ l1 = gcry_sexp_find_token (key, "shadowed-private-key", 0);
+ if (!l1)
+ l1 = gcry_sexp_find_token (key, "public-key", 0);
+ if (!l1)
+ return 0; /* Does not contain a key object. */
+ l2 = gcry_sexp_cadr (l1);
+ gcry_sexp_release (l1);
+ l1 = gcry_sexp_find_token (l2, "q", 1);
+ gcry_sexp_release (l2);
+ if (!l1)
+ return 0; /* Invalid object. */
+ q = gcry_sexp_nth_mpi (l1, 1, GCRYMPI_FMT_USG);
+ gcry_sexp_release (l1);
+ if (!q)
+ return 0; /* Missing value. */
+ nbits = gcry_mpi_get_nbits (q);
+ gcry_mpi_release (q);
+
+ return nbits;
+}
+
+
+/* Return an appropriate hash algorithm to be used with RFC-6979 for a
+ message digest of length MDLEN. Although a fallback of SHA-256 is
+ used the current implementation in Libgcrypt will reject a hash
+ algorithm which does not match the length of the message. */
+static const char *
+rfc6979_hash_algo_string (size_t mdlen)
+{
+ switch (mdlen)
+ {
+ case 20: return "sha1";
+ case 28: return "sha224";
+ case 32: return "sha256";
+ case 48: return "sha384";
+ case 64: return "sha512";
+ default: return "sha256";
+ }
+}
+
+
+/* Encode a message digest for use with the EdDSA algorithm
+ (i.e. curve Ed25519). */
+static gpg_error_t
+do_encode_eddsa (const byte *md, size_t mdlen, gcry_sexp_t *r_hash)
+{
+ gpg_error_t err;
+ gcry_sexp_t hash;
+
+ *r_hash = NULL;
+ err = gcry_sexp_build (&hash, NULL,
+ "(data(flags eddsa)(hash-algo sha512)(value %b))",
+ (int)mdlen, md);
+ if (!err)
+ *r_hash = hash;
+ return err;
+}
+
+
+/* Encode a message digest for use with an DSA algorithm. */
+static gpg_error_t
+do_encode_dsa (const byte *md, size_t mdlen, int pkalgo, gcry_sexp_t pkey,
+ gcry_sexp_t *r_hash)
+{
+ gpg_error_t err;
+ gcry_sexp_t hash;
+ unsigned int qbits;
+
+ *r_hash = NULL;
+
+ if (pkalgo == GCRY_PK_ECDSA)
+ qbits = gcry_pk_get_nbits (pkey);
+ else if (pkalgo == GCRY_PK_DSA)
+ qbits = get_dsa_qbits (pkey);
+ else
+ return gpg_error (GPG_ERR_WRONG_PUBKEY_ALGO);
+
+ if (pkalgo == GCRY_PK_DSA && (qbits%8))
+ {
+ /* FIXME: We check the QBITS but print a message about the hash
+ length. */
+ log_error (_("DSA requires the hash length to be a"
+ " multiple of 8 bits\n"));
+ return gpg_error (GPG_ERR_INV_LENGTH);
+ }
+
+ /* Don't allow any Q smaller than 160 bits. We don't want someone
+ to issue signatures from a key with a 16-bit Q or something like
+ that, which would look correct but allow trivial forgeries. Yes,
+ I know this rules out using MD5 with DSA. ;) */
+ if (qbits < 160)
+ {
+ log_error (_("%s key uses an unsafe (%u bit) hash\n"),
+ gcry_pk_algo_name (pkalgo), qbits);
+ return gpg_error (GPG_ERR_INV_LENGTH);
+ }
+
+ /* ECDSA 521 is special has it is larger than the largest hash
+ we have (SHA-512). Thus we change the size for further
+ processing to 512. */
+ if (pkalgo == GCRY_PK_ECDSA && qbits > 512)
+ qbits = 512;
+
+ /* Check if we're too short. Too long is safe as we'll
+ automatically left-truncate. */
+ if (mdlen < qbits/8)
+ {
+ log_error (_("a %zu bit hash is not valid for a %u bit %s key\n"),
+ mdlen*8,
+ gcry_pk_get_nbits (pkey),
+ gcry_pk_algo_name (pkalgo));
+ return gpg_error (GPG_ERR_INV_LENGTH);
+ }
+
+ /* Truncate. */
+ if (mdlen > qbits/8)
+ mdlen = qbits/8;
+
+ /* Create the S-expression. */
+ err = gcry_sexp_build (&hash, NULL,
+ "(data (flags rfc6979) (hash %s %b))",
+ rfc6979_hash_algo_string (mdlen),
+ (int)mdlen, md);
+ if (!err)
+ *r_hash = hash;
+ return err;
+}
+
+
+/* Special version of do_encode_md to take care of pkcs#1 padding.
+ For TLS-MD5SHA1 we need to do the padding ourself as Libgrypt does
+ not know about this special scheme. Fixme: We should have a
+ pkcs1-only-padding flag for Libgcrypt. */
+static int
+do_encode_raw_pkcs1 (const byte *md, size_t mdlen, unsigned int nbits,
+ gcry_sexp_t *r_hash)
+{
+ int rc;
+ gcry_sexp_t hash;
+ unsigned char *frame;
+ size_t i, n, nframe;
+
+ nframe = (nbits+7) / 8;
+ if ( !mdlen || mdlen + 8 + 4 > nframe )
+ {
+ /* Can't encode this hash into a frame of size NFRAME. */
+ return gpg_error (GPG_ERR_TOO_SHORT);
+ }
+
+ frame = xtrymalloc (nframe);
+ if (!frame)
+ return gpg_error_from_syserror ();
+
+ /* Assemble the pkcs#1 block type 1. */
+ n = 0;
+ frame[n++] = 0;
+ frame[n++] = 1; /* Block type. */
+ i = nframe - mdlen - 3 ;
+ assert (i >= 8); /* At least 8 bytes of padding. */
+ memset (frame+n, 0xff, i );
+ n += i;
+ frame[n++] = 0;
+ memcpy (frame+n, md, mdlen );
+ n += mdlen;
+ assert (n == nframe);
+
+ /* Create the S-expression. */
+ rc = gcry_sexp_build (&hash, NULL,
+ "(data (flags raw) (value %b))",
+ (int)nframe, frame);
+ xfree (frame);
+
+ *r_hash = hash;
+ return rc;
+}
+
+
+
+/* SIGN whatever information we have accumulated in CTRL and return
+ * the signature S-expression. LOOKUP is an optional function to
+ * provide a way for lower layers to ask for the caching TTL. If a
+ * CACHE_NONCE is given that cache item is first tried to get a
+ * passphrase. If OVERRIDEDATA is not NULL, OVERRIDEDATALEN bytes
+ * from this buffer are used instead of the data in CTRL. The
+ * override feature is required to allow the use of Ed25519 with ssh
+ * because Ed25519 does the hashing itself. */
+gpg_error_t
+agent_pksign_do (ctrl_t ctrl, const char *cache_nonce,
+ const char *desc_text,
+ gcry_sexp_t *signature_sexp,
+ cache_mode_t cache_mode, lookup_ttl_t lookup_ttl,
+ const void *overridedata, size_t overridedatalen)
+{
+ gpg_error_t err = 0;
+ gcry_sexp_t s_skey = NULL;
+ gcry_sexp_t s_sig = NULL;
+ gcry_sexp_t s_hash = NULL;
+ gcry_sexp_t s_pkey = NULL;
+ unsigned char *shadow_info = NULL;
+ const unsigned char *data;
+ int datalen;
+ int check_signature = 0;
+
+ if (overridedata)
+ {
+ data = overridedata;
+ datalen = overridedatalen;
+ }
+ else
+ {
+ data = ctrl->digest.value;
+ datalen = ctrl->digest.valuelen;
+ }
+
+ if (!ctrl->have_keygrip)
+ return gpg_error (GPG_ERR_NO_SECKEY);
+
+ err = agent_key_from_file (ctrl, cache_nonce, desc_text, ctrl->keygrip,
+ &shadow_info, cache_mode, lookup_ttl,
+ &s_skey, NULL);
+ if (err)
+ {
+ if (gpg_err_code (err) != GPG_ERR_NO_SECKEY)
+ log_error ("failed to read the secret key\n");
+ goto leave;
+ }
+
+ if (shadow_info)
+ {
+ /* Divert operation to the smartcard */
+ size_t len;
+ unsigned char *buf = NULL;
+ int key_type;
+ int is_RSA = 0;
+ int is_ECDSA = 0;
+ int is_EdDSA = 0;
+
+ err = agent_public_key_from_file (ctrl, ctrl->keygrip, &s_pkey);
+ if (err)
+ {
+ log_error ("failed to read the public key\n");
+ goto leave;
+ }
+
+ if (agent_is_eddsa_key (s_skey))
+ is_EdDSA = 1;
+ else
+ {
+ key_type = agent_is_dsa_key (s_skey);
+ if (key_type == 0)
+ is_RSA = 1;
+ else if (key_type == GCRY_PK_ECDSA)
+ is_ECDSA = 1;
+ }
+
+ {
+ char *desc2 = NULL;
+
+ if (desc_text)
+ agent_modify_description (desc_text, NULL, s_skey, &desc2);
+
+ err = divert_pksign (ctrl, desc2? desc2 : desc_text,
+ data, datalen,
+ ctrl->digest.algo,
+ ctrl->keygrip,
+ shadow_info, &buf, &len);
+ xfree (desc2);
+ }
+ if (err)
+ {
+ log_error ("smartcard signing failed: %s\n", gpg_strerror (err));
+ goto leave;
+ }
+
+ if (is_RSA)
+ {
+ check_signature = 1;
+ if (*buf & 0x80)
+ {
+ len++;
+ buf = xtryrealloc (buf, len);
+ if (!buf)
+ goto leave;
+
+ memmove (buf + 1, buf, len - 1);
+ *buf = 0;
+ }
+
+ err = gcry_sexp_build (&s_sig, NULL, "(sig-val(rsa(s%b)))",
+ (int)len, buf);
+ }
+ else if (is_EdDSA)
+ {
+ err = gcry_sexp_build (&s_sig, NULL, "(sig-val(eddsa(r%b)(s%b)))",
+ (int)len/2, buf, (int)len/2, buf + len/2);
+ }
+ else if (is_ECDSA)
+ {
+ unsigned char *r_buf_allocated = NULL;
+ unsigned char *s_buf_allocated = NULL;
+ unsigned char *r_buf, *s_buf;
+ int r_buflen, s_buflen;
+
+ r_buflen = s_buflen = len/2;
+
+ if (*buf & 0x80)
+ {
+ r_buflen++;
+ r_buf_allocated = xtrymalloc (r_buflen);
+ if (!r_buf_allocated)
+ {
+ err = gpg_error_from_syserror ();
+ goto leave;
+ }
+
+ r_buf = r_buf_allocated;
+ memcpy (r_buf + 1, buf, len/2);
+ *r_buf = 0;
+ }
+ else
+ r_buf = buf;
+
+ if (*(buf + len/2) & 0x80)
+ {
+ s_buflen++;
+ s_buf_allocated = xtrymalloc (s_buflen);
+ if (!s_buf_allocated)
+ {
+ err = gpg_error_from_syserror ();
+ xfree (r_buf_allocated);
+ goto leave;
+ }
+
+ s_buf = s_buf_allocated;
+ memcpy (s_buf + 1, buf + len/2, len/2);
+ *s_buf = 0;
+ }
+ else
+ s_buf = buf + len/2;
+
+ err = gcry_sexp_build (&s_sig, NULL, "(sig-val(ecdsa(r%b)(s%b)))",
+ r_buflen, r_buf,
+ s_buflen, s_buf);
+ xfree (r_buf_allocated);
+ xfree (s_buf_allocated);
+ }
+ else
+ err = gpg_error (GPG_ERR_NOT_IMPLEMENTED);
+
+ xfree (buf);
+ if (err)
+ {
+ log_error ("failed to convert sigbuf returned by divert_pksign "
+ "into S-Exp: %s", gpg_strerror (err));
+ goto leave;
+ }
+ }
+ else
+ {
+ /* No smartcard, but a private key */
+ int dsaalgo = 0;
+
+ /* Put the hash into a sexp */
+ if (agent_is_eddsa_key (s_skey))
+ err = do_encode_eddsa (data, datalen,
+ &s_hash);
+ else if (ctrl->digest.algo == MD_USER_TLS_MD5SHA1)
+ err = do_encode_raw_pkcs1 (data, datalen,
+ gcry_pk_get_nbits (s_skey),
+ &s_hash);
+ else if ( (dsaalgo = agent_is_dsa_key (s_skey)) )
+ err = do_encode_dsa (data, datalen,
+ dsaalgo, s_skey,
+ &s_hash);
+ else
+ err = do_encode_md (data, datalen,
+ ctrl->digest.algo,
+ &s_hash,
+ ctrl->digest.raw_value);
+ if (err)
+ goto leave;
+
+ if (DBG_CRYPTO)
+ {
+ gcry_log_debugsxp ("skey", s_skey);
+ gcry_log_debugsxp ("hash", s_hash);
+ }
+
+ /* sign */
+ err = gcry_pk_sign (&s_sig, s_hash, s_skey);
+ if (err)
+ {
+ log_error ("signing failed: %s\n", gpg_strerror (err));
+ goto leave;
+ }
+
+ if (DBG_CRYPTO)
+ gcry_log_debugsxp ("rslt", s_sig);
+ }
+
+ /* Check that the signature verification worked and nothing is
+ * fooling us e.g. by a bug in the signature create code or by
+ * deliberately introduced faults. Because Libgcrypt 1.7 does this
+ * for RSA internally there is no need to do it here again. */
+ if (check_signature)
+ {
+ gcry_sexp_t sexp_key = s_pkey? s_pkey: s_skey;
+
+ if (s_hash == NULL)
+ {
+ if (ctrl->digest.algo == MD_USER_TLS_MD5SHA1)
+ err = do_encode_raw_pkcs1 (data, datalen,
+ gcry_pk_get_nbits (sexp_key), &s_hash);
+ else
+ err = do_encode_md (data, datalen, ctrl->digest.algo, &s_hash,
+ ctrl->digest.raw_value);
+ }
+
+ if (!err)
+ err = gcry_pk_verify (s_sig, s_hash, sexp_key);
+
+ if (err)
+ {
+ log_error (_("checking created signature failed: %s\n"),
+ gpg_strerror (err));
+ gcry_sexp_release (s_sig);
+ s_sig = NULL;
+ }
+ }
+
+ leave:
+
+ *signature_sexp = s_sig;
+
+ gcry_sexp_release (s_pkey);
+ gcry_sexp_release (s_skey);
+ gcry_sexp_release (s_hash);
+ xfree (shadow_info);
+
+ return err;
+}
+
+
+/* SIGN whatever information we have accumulated in CTRL and write it
+ * back to OUTFP. If a CACHE_NONCE is given that cache item is first
+ * tried to get a passphrase. */
+gpg_error_t
+agent_pksign (ctrl_t ctrl, const char *cache_nonce, const char *desc_text,
+ membuf_t *outbuf, cache_mode_t cache_mode)
+{
+ gpg_error_t err;
+ gcry_sexp_t s_sig = NULL;
+ char *buf = NULL;
+ size_t len = 0;
+
+ err = agent_pksign_do (ctrl, cache_nonce, desc_text, &s_sig, cache_mode,
+ NULL, NULL, 0);
+ if (err)
+ goto leave;
+
+ len = gcry_sexp_sprint (s_sig, GCRYSEXP_FMT_CANON, NULL, 0);
+ log_assert (len);
+ buf = xtrymalloc (len);
+ if (!buf)
+ {
+ err = gpg_error_from_syserror ();
+ goto leave;
+ }
+ len = gcry_sexp_sprint (s_sig, GCRYSEXP_FMT_CANON, buf, len);
+ log_assert (len);
+ put_membuf (outbuf, buf, len);
+
+ leave:
+ gcry_sexp_release (s_sig);
+ xfree (buf);
+
+ return err;
+}
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