--- a/cli-authpubkey.c	Thu Mar 21 23:28:59 2019 +0800
+++ b/cli-authpubkey.c	Fri Jun 26 21:07:34 2020 +0800
@@ -33,7 +33,7 @@
 #include "agentfwd.h"
 
 #if DROPBEAR_CLI_PUBKEY_AUTH
-static void send_msg_userauth_pubkey(sign_key *key, int type, int realsign);
+static void send_msg_userauth_pubkey(sign_key *key, enum signature_type sigtype, int realsign);
 
 /* Called when we receive a SSH_MSG_USERAUTH_FAILURE for a pubkey request.
  * We use it to remove the key we tried from the list */
@@ -59,13 +59,15 @@
 	char* algotype = NULL;
 	unsigned int algolen;
 	enum signkey_type keytype;
+	enum signature_type sigtype;
 	unsigned int remotelen;
 
 	TRACE(("enter recv_msg_userauth_pk_ok"))
 
 	algotype = buf_getstring(ses.payload, &algolen);
-	keytype = signkey_type_from_name(algotype, algolen);
-	TRACE(("recv_msg_userauth_pk_ok: type %d", keytype))
+	sigtype = signature_type_from_name(algotype, algolen);
+	keytype = signkey_type_from_signature(sigtype);
+	TRACE(("recv_msg_userauth_pk_ok: type %d", sigtype))
 	m_free(algotype);
 
 	keybuf = buf_new(MAX_PUBKEY_SIZE);
@@ -112,7 +114,7 @@
 		TRACE(("matching key"))
 		/* XXX TODO: if it's an encrypted key, here we ask for their
 		 * password */
-		send_msg_userauth_pubkey((sign_key*)iter->item, keytype, 1);
+		send_msg_userauth_pubkey((sign_key*)iter->item, sigtype, 1);
 	} else {
 		TRACE(("That was whacky. We got told that a key was valid, but it didn't match our list. Sounds like dodgy code on Dropbear's part"))
 	}
@@ -120,31 +122,32 @@
 	TRACE(("leave recv_msg_userauth_pk_ok"))
 }
 
-void cli_buf_put_sign(buffer* buf, sign_key *key, int type, 
+static void cli_buf_put_sign(buffer* buf, sign_key *key, enum signature_type sigtype,
 			const buffer *data_buf) {
 #if DROPBEAR_CLI_AGENTFWD
+	// TODO: rsa-sha256 agent
 	if (key->source == SIGNKEY_SOURCE_AGENT) {
 		/* Format the agent signature ourselves, as buf_put_sign would. */
 		buffer *sigblob;
 		sigblob = buf_new(MAX_PUBKEY_SIZE);
-		agent_buf_sign(sigblob, key, data_buf);
+		agent_buf_sign(sigblob, key, data_buf, sigtype);
 		buf_putbufstring(buf, sigblob);
 		buf_free(sigblob);
 	} else 
 #endif /* DROPBEAR_CLI_AGENTFWD */
 	{
-		buf_put_sign(buf, key, type, data_buf);
+		buf_put_sign(buf, key, sigtype, data_buf);
 	}
 }
 
-/* TODO: make it take an agent reference to use as well */
-static void send_msg_userauth_pubkey(sign_key *key, int type, int realsign) {
+static void send_msg_userauth_pubkey(sign_key *key, enum signature_type sigtype, int realsign) {
 
 	const char *algoname = NULL;
 	unsigned int algolen;
 	buffer* sigbuf = NULL;
+	enum signkey_type keytype = signkey_type_from_signature(sigtype);
 
-	TRACE(("enter send_msg_userauth_pubkey"))
+	TRACE(("enter send_msg_userauth_pubkey sigtype %d", sigtype))
 	CHECKCLEARTOWRITE();
 
 	buf_putbyte(ses.writepayload, SSH_MSG_USERAUTH_REQUEST);
@@ -160,10 +163,9 @@
 
 	buf_putbyte(ses.writepayload, realsign);
 
-	algoname = signkey_name_from_type(type, &algolen);
-
+	algoname = signature_name_from_type(sigtype, &algolen);
 	buf_putstring(ses.writepayload, algoname, algolen);
-	buf_put_pub_key(ses.writepayload, key, type);
+	buf_put_pub_key(ses.writepayload, key, keytype);
 
 	if (realsign) {
 		TRACE(("realsign"))
@@ -172,7 +174,7 @@
 		sigbuf = buf_new(4 + ses.session_id->len + ses.writepayload->len);
 		buf_putbufstring(sigbuf, ses.session_id);
 		buf_putbytes(sigbuf, ses.writepayload->data, ses.writepayload->len);
-		cli_buf_put_sign(ses.writepayload, key, type, sigbuf);
+		cli_buf_put_sign(ses.writepayload, key, sigtype, sigbuf);
 		buf_free(sigbuf); /* Nothing confidential in the buffer */
 	}
 
@@ -182,7 +184,7 @@
 
 /* Returns 1 if a key was tried */
 int cli_auth_pubkey() {
-
+	enum signature_type sigtype = DROPBEAR_SIGNATURE_NONE;
 	TRACE(("enter cli_auth_pubkey"))
 
 #if DROPBEAR_CLI_AGENTFWD
@@ -190,13 +192,79 @@
 		/* get the list of available keys from the agent */
 		cli_load_agent_keys(cli_opts.privkeys);
 		cli_opts.agent_keys_loaded = 1;
+		TRACE(("cli_auth_pubkey: agent keys loaded"))
 	}
 #endif
 
+	/* iterate through privkeys to remove ones not allowed in server-sig-algs */
+ 	while (cli_opts.privkeys->first) {
+		sign_key * key = (sign_key*)cli_opts.privkeys->first->item;
+		if (cli_ses.server_sig_algs) {
+#if DROPBEAR_RSA
+			if (key->type == DROPBEAR_SIGNKEY_RSA) {
+#if DROPBEAR_RSA_SHA256
+				if (buf_has_algo(cli_ses.server_sig_algs, SSH_SIGNATURE_RSA_SHA256) 
+						== DROPBEAR_SUCCESS) {
+					sigtype = DROPBEAR_SIGNATURE_RSA_SHA256;
+					TRACE(("server-sig-algs allows rsa sha256"))
+					break;
+				}
+#endif /* DROPBEAR_RSA_SHA256 */
+#if DROPBEAR_RSA_SHA1
+				if (buf_has_algo(cli_ses.server_sig_algs, SSH_SIGNKEY_RSA)
+						== DROPBEAR_SUCCESS) {
+					sigtype = DROPBEAR_SIGNATURE_RSA_SHA1;
+					TRACE(("server-sig-algs allows rsa sha1"))
+					break;
+				}
+#endif /* DROPBEAR_RSA_SHA256 */
+			} else
+#endif /* DROPBEAR_RSA */
+			{
+				/* Not RSA */
+				const char *name = NULL;
+				sigtype = signature_type_from_signkey(key->type);
+				name = signature_name_from_type(sigtype, NULL);
+				if (buf_has_algo(cli_ses.server_sig_algs, name)
+						== DROPBEAR_SUCCESS) {
+					TRACE(("server-sig-algs allows %s", name))
+					break;
+				}
+			}
+
+			/* No match, skip this key */
+			TRACE(("server-sig-algs no match keytype %d, skipping", key->type))
+			key = list_remove(cli_opts.privkeys->first);
+			sign_key_free(key); 
+			continue;
+		} else {
+			/* Server didn't provide a server-sig-algs list, we'll 
+			   assume all except rsa-sha256 are OK. */
+#if DROPBEAR_RSA
+			if (key->type == DROPBEAR_SIGNKEY_RSA) {
+#if DROPBEAR_RSA_SHA1
+				sigtype = DROPBEAR_SIGNATURE_RSA_SHA1;
+				TRACE(("no server-sig-algs, using rsa sha1"))
+				break;
+#else
+				/* only support rsa-sha256, skip this key */
+				TRACE(("no server-sig-algs, skipping rsa sha256"))
+				key = list_remove(cli_opts.privkeys->first);
+				sign_key_free(key); 
+				continue;
+#endif
+			} /* key->type == DROPBEAR_SIGNKEY_RSA */
+#endif /* DROPBEAR_RSA */
+			sigtype = signature_type_from_signkey(key->type);
+			TRACE(("no server-sig-algs, using key"))
+			break;
+		}
+	}
+
 	if (cli_opts.privkeys->first) {
 		sign_key * key = (sign_key*)cli_opts.privkeys->first->item;
 		/* Send a trial request */
-		send_msg_userauth_pubkey(key, key->type, 0);
+		send_msg_userauth_pubkey(key, sigtype, 0);
 		cli_ses.lastprivkey = key;
 		TRACE(("leave cli_auth_pubkey-success"))
 		return 1;