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Fix handling of RSA + SHA-2 certified host keys.

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Initial live testing pointed out that the ssh_keyalg corresponding to
the certified version of rsa-sha2-512 was expecting to see the SSH id
string "rsa-sha2-512-cert-v01@openssh.com" at the start of the public
key blob, whereas in fact, the _key_ type identifier is still
"ssh-rsa-...", just as the key type for base rsa-sha2-512 is base
ssh-rsa.

Fixed inside openssh-certs.c, by adding a couple more strings to the
'extra' structure.
This commit is contained in:
Simon Tatham 2022-04-27 07:44:27 +01:00
parent 3bb7e6ba9e
commit de5f295b99
1 changed files with 34 additions and 15 deletions
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49
crypto/openssh-certs.c
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@ -66,6 +66,22 @@ typedef struct opensshcert_extra {
* string itself. * string itself.
*/ */
blob_fmt pub_fmt, base_ossh_fmt, cert_ossh_fmt; blob_fmt pub_fmt, base_ossh_fmt, cert_ossh_fmt;
/*
* The RSA-SHA2 algorithm names have their SSH id set to names
* like "rsa-sha2-512-cert-...", which is what will be received in
* the KEXINIT algorithm list if a host key in one of those
* algorithms is presented. But the _key_ type id that will appear
* in the public key blob is "ssh-rsa-cert-...". So we need a
* separate field to indicate the key type id we expect to see in
* certified public keys, and also the one we want to put back
* into the artificial public blob we make to pass to the
* constructor for the underlying key.
*
* (In rsa.c this is managed much more simply, because everything
* sharing the same vtable wants the same key type id.)
*/
const char *cert_key_ssh_id, *base_key_ssh_id;
} opensshcert_extra; } opensshcert_extra;
/* /*
@ -206,18 +222,18 @@ static const ssh_keyalg *opensshcert_related_alg(const ssh_keyalg *self,
* macro so I can also make an array of them all. * macro so I can also make an array of them all.
*/ */
#define KEYALG_LIST(X) \ #define KEYALG_LIST(X) \
X(ssh_dsa, "ssh-dss", dsa) \ X(ssh_dsa, "ssh-dss", "ssh-dss", dsa) \
X(ssh_rsa, "ssh-rsa", rsa) \ X(ssh_rsa, "ssh-rsa", "ssh-rsa", rsa) \
X(ssh_rsa_sha256, "rsa-sha2-256", rsa) \ X(ssh_rsa_sha256, "rsa-sha2-256", "ssh-rsa", rsa) \
X(ssh_rsa_sha512, "rsa-sha2-512", rsa) \ X(ssh_rsa_sha512, "rsa-sha2-512", "ssh-rsa", rsa) \
X(ssh_ecdsa_ed25519, "ssh-ed25519", eddsa) \ X(ssh_ecdsa_ed25519, "ssh-ed25519", "ssh-ed25519", eddsa) \
X(ssh_ecdsa_nistp256, "ecdsa-sha2-nistp256", ecdsa) \ X(ssh_ecdsa_nistp256, "ecdsa-sha2-nistp256","ecdsa-sha2-nistp256", ecdsa) \
X(ssh_ecdsa_nistp384, "ecdsa-sha2-nistp384", ecdsa) \ X(ssh_ecdsa_nistp384, "ecdsa-sha2-nistp384","ecdsa-sha2-nistp384", ecdsa) \
X(ssh_ecdsa_nistp521, "ecdsa-sha2-nistp521", ecdsa) \ X(ssh_ecdsa_nistp521, "ecdsa-sha2-nistp521","ecdsa-sha2-nistp521", ecdsa) \
/* end of list */ /* end of list */
#define KEYALG_DEF(name, ssh_id_prefix, fmt_prefix) \ #define KEYALG_DEF(name, ssh_alg_id_prefix, ssh_key_id_prefix, fmt_prefix) \
const struct opensshcert_extra opensshcert_##name##_extra = { \ const struct opensshcert_extra opensshcert_##name##_extra = { \
.pub_fmt = { .fmt = fmt_prefix ## _pub_fmt, \ .pub_fmt = { .fmt = fmt_prefix ## _pub_fmt, \
.len = lenof(fmt_prefix ## _pub_fmt) }, \ .len = lenof(fmt_prefix ## _pub_fmt) }, \
@ -225,6 +241,8 @@ static const ssh_keyalg *opensshcert_related_alg(const ssh_keyalg *self,
.len = lenof(fmt_prefix ## _base_ossh_fmt) }, \ .len = lenof(fmt_prefix ## _base_ossh_fmt) }, \
.cert_ossh_fmt = { .fmt = fmt_prefix ## _cert_ossh_fmt, \ .cert_ossh_fmt = { .fmt = fmt_prefix ## _cert_ossh_fmt, \
.len = lenof(fmt_prefix ## _cert_ossh_fmt) }, \ .len = lenof(fmt_prefix ## _cert_ossh_fmt) }, \
.cert_key_ssh_id = ssh_key_id_prefix "-cert-v01@openssh.com", \
.base_key_ssh_id = ssh_key_id_prefix, \
}; \ }; \
\ \
const ssh_keyalg opensshcert_##name = { \ const ssh_keyalg opensshcert_##name = { \
@ -249,7 +267,7 @@ static const ssh_keyalg *opensshcert_related_alg(const ssh_keyalg *self,
.supported_flags = opensshcert_supported_flags, \ .supported_flags = opensshcert_supported_flags, \
.alternate_ssh_id = opensshcert_alternate_ssh_id, \ .alternate_ssh_id = opensshcert_alternate_ssh_id, \
.related_alg = opensshcert_related_alg, \ .related_alg = opensshcert_related_alg, \
.ssh_id = ssh_id_prefix "-cert-v01@openssh.com", \ .ssh_id = ssh_alg_id_prefix "-cert-v01@openssh.com", \
.cache_id = NULL, \ .cache_id = NULL, \
.extra = &opensshcert_##name##_extra, \ .extra = &opensshcert_##name##_extra, \
.is_certificate = true, \ .is_certificate = true, \
@ -258,7 +276,7 @@ static const ssh_keyalg *opensshcert_related_alg(const ssh_keyalg *self,
KEYALG_LIST(KEYALG_DEF) KEYALG_LIST(KEYALG_DEF)
#undef KEYALG_DEF #undef KEYALG_DEF
#define KEYALG_LIST_ENTRY(name, ssh_id_prefix, fmt_prefix) &opensshcert_##name, #define KEYALG_LIST_ENTRY(name, algid, keyid, fmt) &opensshcert_##name,
static const ssh_keyalg *const opensshcert_all_keyalgs[] = { static const ssh_keyalg *const opensshcert_all_keyalgs[] = {
KEYALG_LIST(KEYALG_LIST_ENTRY) KEYALG_LIST(KEYALG_LIST_ENTRY)
}; };
@ -273,7 +291,7 @@ static opensshcert_key *opensshcert_new_shared(
BinarySource_BARE_INIT_PL(src, blob); BinarySource_BARE_INIT_PL(src, blob);
/* Check the initial key-type string */ /* Check the initial key-type string */
if (!ptrlen_eq_string(get_string(src), self->ssh_id)) if (!ptrlen_eq_string(get_string(src), extra->cert_key_ssh_id))
return NULL; return NULL;
opensshcert_key *ck = snew(opensshcert_key); opensshcert_key *ck = snew(opensshcert_key);
@ -283,7 +301,7 @@ static opensshcert_key *opensshcert_new_shared(
ck->nonce = strbuf_dup(get_string(src)); ck->nonce = strbuf_dup(get_string(src));
strbuf *basepub = strbuf_new(); strbuf *basepub = strbuf_new();
{ {
put_stringz(basepub, self->base_alg->ssh_id); put_stringz(basepub, extra->base_key_ssh_id);
/* Make the base public key blob out of the public key /* Make the base public key blob out of the public key
* material in the certificate. This invocation of the * material in the certificate. This invocation of the
@ -461,7 +479,8 @@ static ssh_key *opensshcert_ca_pub_key(
static void opensshcert_signature_preimage(opensshcert_key *ck, BinarySink *bs) static void opensshcert_signature_preimage(opensshcert_key *ck, BinarySink *bs)
{ {
put_stringz(bs, ck->sshk.vt->ssh_id); const opensshcert_extra *extra = ck->sshk.vt->extra;
put_stringz(bs, extra->cert_key_ssh_id);
put_stringpl(bs, ptrlen_from_strbuf(ck->nonce)); put_stringpl(bs, ptrlen_from_strbuf(ck->nonce));
strbuf *basepub = strbuf_new(); strbuf *basepub = strbuf_new();