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ssh: Simplify the curve name lookup.

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* agent/command-ssh.c (struct ssh_key_type_spec): Add field
alt_curve_name.
(ssh_key_types): Add some alternate curve names.
(ssh_identifier_from_curve_name): Lookup also bey alternative names
and return the canonical name.
(ssh_key_to_blob): Simplify the ECDSA case by using gcry_pk_get_curve
instead of the explicit mapping.
(ssh_receive_key): Likewise.  Use ssh_identifier_from_curve_name to
validate the curve name.  Remove the reverse mapping because since
GnuPG-2.2 Libgcrypt 1.7 is required.
(ssh_handler_request_identities): Log an error message.
--

This change will make it easier to support other curves, in particular
those from tokens.  Libgcrypt has a large list of alias names which we
now use to to make the mapping more flexible.

Signed-off-by: Werner Koch <wk@gnupg.org>
This commit is contained in:
Werner Koch 2019-01-17 15:42:33 +01:00
parent dafffa95b2
commit d93797c8a7
No known key found for this signature in database
GPG Key ID: E3FDFF218E45B72B
1 changed files with 54 additions and 84 deletions
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138
agent/command-ssh.c
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@ -195,9 +195,14 @@ struct ssh_key_type_spec
algorithm. */
ssh_signature_encoder_t signature_encoder;
/* The name of the ECC curve or NULL. */
/* The name of the ECC curve or NULL for non-ECC algos. This is the
* canonical name for the curve as specified by RFC-5656. */
const char *curve_name;
/* An alias for curve_name or NULL. Actually this is Libcgrypt's
* primary name of the curve. */
const char *alt_curve_name;
/* The hash algorithm to be used with this key. 0 for using the
default. */
int hash_algo;
@ -297,68 +302,71 @@ static const ssh_key_type_spec_t ssh_key_types[] =
{
"ssh-ed25519", "Ed25519", GCRY_PK_EDDSA, "qd", "q", "rs", "qd",
NULL, ssh_signature_encoder_eddsa,
"Ed25519", 0, SPEC_FLAG_IS_EdDSA
"Ed25519", NULL, 0, SPEC_FLAG_IS_EdDSA
},
{
"ssh-rsa", "RSA", GCRY_PK_RSA, "nedupq", "en", "s", "nedpqu",
ssh_key_modifier_rsa, ssh_signature_encoder_rsa,
NULL, 0, SPEC_FLAG_USE_PKCS1V2
NULL, NULL, 0, SPEC_FLAG_USE_PKCS1V2
},
{
"ssh-dss", "DSA", GCRY_PK_DSA, "pqgyx", "pqgy", "rs", "pqgyx",
NULL, ssh_signature_encoder_dsa,
NULL, 0, 0
NULL, NULL, 0, 0
},
{
"ecdsa-sha2-nistp256", "ECDSA", GCRY_PK_ECC, "qd", "q", "rs", "qd",
NULL, ssh_signature_encoder_ecdsa,
"nistp256", GCRY_MD_SHA256, SPEC_FLAG_IS_ECDSA
"nistp256", "NIST P-256", GCRY_MD_SHA256, SPEC_FLAG_IS_ECDSA
},
{
"ecdsa-sha2-nistp384", "ECDSA", GCRY_PK_ECC, "qd", "q", "rs", "qd",
NULL, ssh_signature_encoder_ecdsa,
"nistp384", GCRY_MD_SHA384, SPEC_FLAG_IS_ECDSA
"nistp384", "NIST P-384", GCRY_MD_SHA384, SPEC_FLAG_IS_ECDSA
},
{
"ecdsa-sha2-nistp521", "ECDSA", GCRY_PK_ECC, "qd", "q", "rs", "qd",
NULL, ssh_signature_encoder_ecdsa,
"nistp521", GCRY_MD_SHA512, SPEC_FLAG_IS_ECDSA
"nistp521", "NIST P-521", GCRY_MD_SHA512, SPEC_FLAG_IS_ECDSA
},
{
"ssh-ed25519-cert-v01@openssh.com", "Ed25519",
GCRY_PK_EDDSA, "qd", "q", "rs", "qd",
NULL, ssh_signature_encoder_eddsa,
"Ed25519", 0, SPEC_FLAG_IS_EdDSA | SPEC_FLAG_WITH_CERT
"Ed25519", NULL, 0, SPEC_FLAG_IS_EdDSA | SPEC_FLAG_WITH_CERT
},
{
"ssh-rsa-cert-v01@openssh.com", "RSA",
GCRY_PK_RSA, "nedupq", "en", "s", "nedpqu",
ssh_key_modifier_rsa, ssh_signature_encoder_rsa,
NULL, 0, SPEC_FLAG_USE_PKCS1V2 | SPEC_FLAG_WITH_CERT
NULL, NULL, 0, SPEC_FLAG_USE_PKCS1V2 | SPEC_FLAG_WITH_CERT
},
{
"ssh-dss-cert-v01@openssh.com", "DSA",
GCRY_PK_DSA, "pqgyx", "pqgy", "rs", "pqgyx",
NULL, ssh_signature_encoder_dsa,
NULL, 0, SPEC_FLAG_WITH_CERT | SPEC_FLAG_WITH_CERT
NULL, NULL, 0, SPEC_FLAG_WITH_CERT | SPEC_FLAG_WITH_CERT
},
{
"ecdsa-sha2-nistp256-cert-v01@openssh.com", "ECDSA",
GCRY_PK_ECC, "qd", "q", "rs", "qd",
NULL, ssh_signature_encoder_ecdsa,
"nistp256", GCRY_MD_SHA256, SPEC_FLAG_IS_ECDSA | SPEC_FLAG_WITH_CERT
"nistp256", "NIST P-256", GCRY_MD_SHA256,
SPEC_FLAG_IS_ECDSA | SPEC_FLAG_WITH_CERT
},
{
"ecdsa-sha2-nistp384-cert-v01@openssh.com", "ECDSA",
GCRY_PK_ECC, "qd", "q", "rs", "qd",
NULL, ssh_signature_encoder_ecdsa,
"nistp384", GCRY_MD_SHA384, SPEC_FLAG_IS_ECDSA | SPEC_FLAG_WITH_CERT
"nistp384", "NIST P-384", GCRY_MD_SHA384,
SPEC_FLAG_IS_ECDSA | SPEC_FLAG_WITH_CERT
},
{
"ecdsa-sha2-nistp521-cert-v01@openssh.com", "ECDSA",
GCRY_PK_ECC, "qd", "q", "rs", "qd",
NULL, ssh_signature_encoder_ecdsa,
"nistp521", GCRY_MD_SHA512, SPEC_FLAG_IS_ECDSA | SPEC_FLAG_WITH_CERT
"nistp521", "NIST P-521", GCRY_MD_SHA512,
SPEC_FLAG_IS_ECDSA | SPEC_FLAG_WITH_CERT
}
};
@ -389,16 +397,24 @@ realloc_secure (void *a, size_t n)
/* Lookup the ssh-identifier for the ECC curve CURVE_NAME. Returns
NULL if not found. */
* NULL if not found. If found the ssh indetifier is returned and a
* pointer to the canonical curve name as specified for ssh is stored
* at R_CANON_NAME. */
static const char *
ssh_identifier_from_curve_name (const char *curve_name)
ssh_identifier_from_curve_name (const char *curve_name,
const char **r_canon_name)
{
int i;
for (i = 0; i < DIM (ssh_key_types); i++)
if (ssh_key_types[i].curve_name
&& !strcmp (ssh_key_types[i].curve_name, curve_name))
return ssh_key_types[i].ssh_identifier;
&& (!strcmp (ssh_key_types[i].curve_name, curve_name)
|| (ssh_key_types[i].alt_curve_name
&& !strcmp (ssh_key_types[i].alt_curve_name, curve_name))))
{
*r_canon_name = ssh_key_types[i].curve_name;
return ssh_key_types[i].ssh_identifier;
}
return NULL;
}
@ -1849,7 +1865,6 @@ ssh_key_to_blob (gcry_sexp_t sexp, int with_secret,
gpg_error_t err = 0;
gcry_sexp_t value_list = NULL;
gcry_sexp_t value_pair = NULL;
char *curve_name = NULL;
estream_t stream = NULL;
void *blob = NULL;
size_t blob_size;
@ -1867,7 +1882,7 @@ ssh_key_to_blob (gcry_sexp_t sexp, int with_secret,
goto out;
}
/* Get the type of the key extpression. */
/* Get the type of the key expression. */
data = gcry_sexp_nth_data (sexp, 0, &datalen);
if (!data)
{
@ -1898,49 +1913,17 @@ ssh_key_to_blob (gcry_sexp_t sexp, int with_secret,
/* Write the ssh algorithm identifier. */
if ((key_spec.flags & SPEC_FLAG_IS_ECDSA))
{
/* Parse the "curve" parameter. We currently expect the curve
name for ECC and not the parameters of the curve. This can
easily be changed but then we need to find the curve name
from the parameters using gcry_pk_get_curve. */
const char *mapped;
const char *sshname;
/* Map the curve name to the ssh name. */
const char *name, *sshname, *canon_name;
gcry_sexp_release (value_pair);
value_pair = gcry_sexp_find_token (value_list, "curve", 5);
if (!value_pair)
{
err = gpg_error (GPG_ERR_INV_CURVE);
goto out;
}
curve_name = gcry_sexp_nth_string (value_pair, 1);
if (!curve_name)
{
err = gpg_error (GPG_ERR_INV_CURVE); /* (Or out of core.) */
goto out;
}
/* Fixme: The mapping should be done by using gcry_pk_get_curve
et al to iterate over all name aliases. */
if (!strcmp (curve_name, "NIST P-256"))
mapped = "nistp256";
else if (!strcmp (curve_name, "NIST P-384"))
mapped = "nistp384";
else if (!strcmp (curve_name, "NIST P-521"))
mapped = "nistp521";
else
mapped = NULL;
if (mapped)
name = gcry_pk_get_curve (sexp, 0, NULL);
if (!name)
{
xfree (curve_name);
curve_name = xtrystrdup (mapped);
if (!curve_name)
{
err = gpg_error_from_syserror ();
goto out;
}
err = gpg_error (GPG_ERR_INV_CURVE);
goto out;
}
sshname = ssh_identifier_from_curve_name (curve_name);
sshname = ssh_identifier_from_curve_name (name, &canon_name);
if (!sshname)
{
err = gpg_error (GPG_ERR_UNKNOWN_CURVE);
@ -1949,7 +1932,7 @@ ssh_key_to_blob (gcry_sexp_t sexp, int with_secret,
err = stream_write_cstring (stream, sshname);
if (err)
goto out;
err = stream_write_cstring (stream, curve_name);
err = stream_write_cstring (stream, canon_name);
if (err)
goto out;
}
@ -2022,7 +2005,6 @@ ssh_key_to_blob (gcry_sexp_t sexp, int with_secret,
out:
gcry_sexp_release (value_list);
gcry_sexp_release (value_pair);
xfree (curve_name);
es_fclose (stream);
es_free (blob);
@ -2081,7 +2063,7 @@ ssh_receive_key (estream_t stream, gcry_sexp_t *key_new, int secret,
ssh_key_type_spec_t spec;
gcry_mpi_t *mpi_list = NULL;
const char *elems;
char *curve_name = NULL;
const char *curve_name = NULL;
err = stream_read_cstring (stream, &key_type);
@ -2204,34 +2186,19 @@ ssh_receive_key (estream_t stream, gcry_sexp_t *key_new, int secret,
* certificate.
*/
unsigned char *buffer;
const char *mapped;
err = stream_read_string (cert? cert : stream, 0, &buffer, NULL);
if (err)
goto out;
curve_name = buffer;
/* Fixme: Check that curve_name matches the keytype. */
/* Because Libgcrypt < 1.6 has no support for the "nistpNNN"
curve names, we need to translate them here to Libgcrypt's
native names. */
if (!strcmp (curve_name, "nistp256"))
mapped = "NIST P-256";
else if (!strcmp (curve_name, "nistp384"))
mapped = "NIST P-384";
else if (!strcmp (curve_name, "nistp521"))
mapped = "NIST P-521";
else
mapped = NULL;
if (mapped)
/* Get the canonical name. Should be the same as the read
* string but we use this mapping to validate that name. */
if (!ssh_identifier_from_curve_name (buffer, &curve_name))
{
xfree (curve_name);
curve_name = xtrystrdup (mapped);
if (!curve_name)
{
err = gpg_error_from_syserror ();
goto out;
}
err = gpg_error (GPG_ERR_UNKNOWN_CURVE);
xfree (buffer);
goto out;
}
xfree (buffer);
err = ssh_receive_mpint_list (stream, secret, &spec, cert, &mpi_list);
if (err)
@ -2299,7 +2266,6 @@ ssh_receive_key (estream_t stream, gcry_sexp_t *key_new, int secret,
out:
es_fclose (cert);
mpint_list_free (mpi_list);
xfree (curve_name);
xfree (key_type);
xfree (comment);
@ -2647,6 +2613,8 @@ ssh_handler_request_identities (ctrl_t ctrl,
continue;
err = ssh_send_key_public (key_blobs, key_public, cardsn);
if (err && opt.verbose)
gcry_log_debugsxp ("pubkey", key_public);
gcry_sexp_release (key_public);
key_public = NULL;
xfree (cardsn);
@ -2722,6 +2690,8 @@ ssh_handler_request_identities (ctrl_t ctrl,
}
else
{
log_error ("ssh request identities failed: %s <%s>\n",
gpg_strerror (err), gpg_strsource (err));
ret_err = stream_write_byte (response, SSH_RESPONSE_FAILURE);
}