auth: Support SHA2 extension for pubkey authentication (RFC 8332)

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/pki.h

@@ -96,6 +96,10 @@ typedef struct ssh_signature_struct *ssh_signature;
 ssh_key ssh_key_dup(const ssh_key key);
 void ssh_key_clean (ssh_key key);
 
+const char *
+ssh_key_get_signature_algorithm(ssh_session session,
+                                enum ssh_keytypes_e type);
+
 /* SSH Signature Functions */
 ssh_signature ssh_signature_new(void);
 void ssh_signature_free(ssh_signature sign);

src/auth.c

@@ -470,6 +470,7 @@ int ssh_userauth_try_publickey(ssh_session session,
                                const ssh_key pubkey)
 {
     ssh_string pubkey_s = NULL;
+    const char *sig_type_c = NULL;
     int rc;
 
     if (session == NULL) {
@@ -506,6 +507,7 @@ int ssh_userauth_try_publickey(ssh_session session,
     if (rc < 0) {
         goto fail;
     }
+    sig_type_c = ssh_key_get_signature_algorithm(session, pubkey->type);
 
     /* request */
     rc = ssh_buffer_pack(session->out_buffer, "bsssbsS",
@@ -514,7 +516,7 @@ int ssh_userauth_try_publickey(ssh_session session,
             "ssh-connection",
             "publickey",
             0, /* private key ? */
-            pubkey->type_c, /* algo */
+            sig_type_c, /* algo */
             pubkey_s /* public key */
             );
     if (rc < 0) {
@@ -575,7 +577,7 @@ int ssh_userauth_publickey(ssh_session session,
 {
     ssh_string str = NULL;
     int rc;
-    const char *type_c;
+    const char *sig_type_c;
     enum ssh_keytypes_e key_type;
 
     if (session == NULL) {
@@ -608,7 +610,7 @@ int ssh_userauth_publickey(ssh_session session,
 
     /* Cert auth requires presenting the cert type name (*-cert@openssh.com) */
     key_type = privkey->cert != NULL ? privkey->cert_type : privkey->type;
-    type_c = ssh_key_type_to_char(key_type);
+    sig_type_c = ssh_key_get_signature_algorithm(session, key_type);
 
     /* get public key or cert */
     rc = ssh_pki_export_pubkey_blob(privkey, &str);
@@ -623,7 +625,7 @@ int ssh_userauth_publickey(ssh_session session,
             "ssh-connection",
             "publickey",
             1, /* private key */
-            type_c, /* algo */
+            sig_type_c, /* algo */
             str /* public key or cert */
             );
     if (rc < 0) {
@@ -673,6 +675,7 @@ static int ssh_userauth_agent_publickey(ssh_session session,
                                         ssh_key pubkey)
 {
     ssh_string str = NULL;
+    const char *sig_type_c = NULL;
     int rc;
 
     switch(session->pending_call_state) {
@@ -700,6 +703,7 @@ static int ssh_userauth_agent_publickey(ssh_session session,
     if (rc < 0) {
         goto fail;
     }
+    sig_type_c = ssh_key_get_signature_algorithm(session, pubkey->type);
 
     /* request */
     rc = ssh_buffer_pack(session->out_buffer, "bsssbsS",
@@ -708,7 +712,7 @@ static int ssh_userauth_agent_publickey(ssh_session session,
             "ssh-connection",
             "publickey",
             1, /* private key */
-            pubkey->type_c, /* algo */
+            sig_type_c, /* algo */
             str /* public key */
             );
     if (rc < 0) {

src/pki.c

@@ -282,8 +282,8 @@ static enum ssh_digest_e ssh_key_hash_from_name(const char *name)
  *
  * @return              A hash type to be used.
  */
-static enum ssh_keytypes_e ssh_key_type_to_hash(ssh_session session,
-                                                enum ssh_keytypes_e type)
+static enum ssh_digest_e ssh_key_type_to_hash(ssh_session session,
+                                       enum ssh_keytypes_e type)
 {
     /* TODO this should also reflect supported key types specified in
      * configuration (ssh_config PubkeyAcceptedKeyTypes) */
@@ -309,6 +309,26 @@ static enum ssh_keytypes_e ssh_key_type_to_hash(ssh_session session,
     return SSH_DIGEST_AUTO;
 }
 
+/**
+ * @brief Gets signature algorithm name to be used with the given
+ *        key type.
+ *
+ * @param[in]  session  SSH session.
+ * @param[in]  type     The algorithm type to convert.
+ *
+ * @return              A string for the keytype or NULL if unknown.
+ */
+const char *
+ssh_key_get_signature_algorithm(ssh_session session,
+                                enum ssh_keytypes_e type)
+{
+    enum ssh_digest_e hash_type;
+
+    hash_type = ssh_key_type_to_hash(session, type);
+
+    return ssh_key_signature_to_char(type, hash_type);
+}
+
 /**
  * @brief Convert a ssh key algorithm name to a ssh key algorithm type.
  *