Fwd: Server accepts key: pkalg rsa-sha2-512 vs ssh-rsa

[Nuno Gonçalves]

On 1/30/2017 3:58 AM, Jakub Jelen wrote:
> This is part of deprecation SHA1 for signatures, which were hardcoded into the core RFCs. The different hashes were introduced in OpenSSH 7.2 [1] and are negotiated using the protocol extension. I
> don't think there are configuration options to control this behavior, but the new algorithms have higher priority for new OpenSSH versions.
>
> [1] http://www.openssh.com/txt/release-7.2
>
> Regards,

In that case this is converted to a bug report: Deprecation of SHA1 is
not being enforced since 7.4p1.

The side effect of this bug is that my "problem" originally reported
disappeared from 7.3p1 to 7.4p1. It was fixed by properly supporting
rsa-sha2-256 from OpenSC (my pkcs11 lib) side, but during tests we
found out that 7.4p1 was not using rsa-sha2-256 anymore.

Bug was introduced with commit:

https://github.com/openssh/openssh-portable/commit/130f5df4fa37cace8c079dccb690e5cafbf00751.

Due to:

https://bugzilla.mindrot.org/show_bug.cgi?id=2547

>From this commit rsa-sha2-256 and rsa-sha2-512 are no longer offered
so all is downgraded to rsa-sha.

A fix applied at current master could be:

diff --git a/kex.c b/kex.c
index a30dabe..13bb9aa 100644
--- a/kex.c
+++ b/kex.c
@@ -348,7 +348,7 @@ kex_send_ext_info(struct ssh *ssh)
  int r;
  char *algs;

- if ((algs = sshkey_alg_list(0, 1, ',')) == NULL)
+ if ((algs = sshkey_alg_list(0, 1, 1, ',')) == NULL)
  return SSH_ERR_ALLOC_FAIL;
  if ((r = sshpkt_start(ssh, SSH2_MSG_EXT_INFO)) != 0 ||
     (r = sshpkt_put_u32(ssh, 1)) != 0 ||
diff --git a/ssh.c b/ssh.c
index ee0b16d..edef335 100644
--- a/ssh.c
+++ b/ssh.c
@@ -684,11 +684,11 @@ main(int ac, char **av)
  else if (strcmp(optarg, "kex") == 0)
  cp = kex_alg_list('\n');
  else if (strcmp(optarg, "key") == 0)
- cp = sshkey_alg_list(0, 0, '\n');
+ cp = sshkey_alg_list(0, 0, 0, '\n');
  else if (strcmp(optarg, "key-cert") == 0)
- cp = sshkey_alg_list(1, 0, '\n');
+ cp = sshkey_alg_list(1, 0, 0, '\n');
  else if (strcmp(optarg, "key-plain") == 0)
- cp = sshkey_alg_list(0, 1, '\n');
+ cp = sshkey_alg_list(0, 1, 0, '\n');
  else if (strcmp(optarg, "protocol-version") == 0) {
 #ifdef WITH_SSH1
  cp = xstrdup("1\n2");
diff --git a/sshkey.c b/sshkey.c
index 31710e5..1c5dfdb 100644
--- a/sshkey.c
+++ b/sshkey.c
@@ -195,14 +195,16 @@ sshkey_ecdsa_nid_from_name(const char *name)
 }

 char *
-sshkey_alg_list(int certs_only, int plain_only, char sep)
+sshkey_alg_list(int certs_only, int plain_only, int sigonly_also, char sep)
 {
  char *tmp, *ret = NULL;
  size_t nlen, rlen = 0;
  const struct keytype *kt;

  for (kt = keytypes; kt->type != -1; kt++) {
- if (kt->name == NULL || kt->sigonly)
+ if (kt->name == NULL)
+ continue;
+ if (!sigonly_also && kt->sigonly)
  continue;
  if ((certs_only && !kt->cert) || (plain_only && kt->cert))
  continue;
diff --git a/sshkey.h b/sshkey.h
index f393638..6a3ff2f 100644
--- a/sshkey.h
+++ b/sshkey.h
@@ -156,7 +156,7 @@ int sshkey_ec_validate_private(const EC_KEY *);
 const char *sshkey_ssh_name(const struct sshkey *);
 const char *sshkey_ssh_name_plain(const struct sshkey *);
 int sshkey_names_valid2(const char *, int);
-char *sshkey_alg_list(int, int, char);
+char *sshkey_alg_list(int, int, int, char);

 int sshkey_from_blob(const u_char *, size_t, struct sshkey **);
 int sshkey_fromb(struct sshbuf *, struct sshkey **);


Thanks,
Nuno