Use find_pubkey_alg in openssh_read_new().

This is better than listing all the algorithm names in yet another
place that will then need updating when a new key format is added.
However, that also means I need to find a new place to put the
'npieces' value I was previously setting up differently per key type;
since that's a fundamental property of the key format, I've moved it
to a constant field in the ssh_signkey structure, and filled that
field in for all the existing key types with the values from the
replaced code in openssh_read_new().

import.c

@@ -1629,7 +1629,7 @@ struct ssh2_userkey *openssh_new_read(const Filename *filename,
     retkey = NULL;
     for (key_index = 0; key_index < key->nkeys; key_index++) {
         unsigned char *thiskey;
-        int thiskeylen, npieces;
+        int thiskeylen;
 
         /*
          * Read the key type, which will tell us how to scan over
@@ -1647,26 +1647,16 @@ struct ssh2_userkey *openssh_new_read(const Filename *filename,
          * of strings, so we just need to know how many of them to
          * skip over. (The numbers below exclude the key comment.)
          */
-        if (match_ssh_id(stringlen, string, "ssh-rsa")) {
-            alg = &ssh_rsa;
-            npieces = 6;           /* n,e,d,iqmp,q,p */
-        } else if (match_ssh_id(stringlen, string, "ssh-dss")) {
-            alg = &ssh_dss;
-            npieces = 5;           /* p,q,g,y,x */
-        } else if (match_ssh_id(stringlen, string,
-                                "ecdsa-sha2-nistp256")) {
-            alg = &ssh_ecdsa_nistp256;
-            npieces = 3;      /* curve name, point, private exponent */
-        } else if (match_ssh_id(stringlen, string,
-                                "ecdsa-sha2-nistp384")) {
-            alg = &ssh_ecdsa_nistp384;
-            npieces = 3;      /* curve name, point, private exponent */
-        } else if (match_ssh_id(stringlen, string,
-                                "ecdsa-sha2-nistp521")) {
-            alg = &ssh_ecdsa_nistp521;
-            npieces = 3;      /* curve name, point, private exponent */
-        } else {
-            errmsg = "private key did not start with type string\n";
+        {
+            /* find_pubkey_alg needs a zero-terminated copy of the
+             * algorithm name */
+            char *name_zt = dupprintf("%.*s", stringlen, (char *)string);
+            alg = find_pubkey_alg(name_zt);
+            sfree(name_zt);
+        }
+
+        if (!alg) {
+            errmsg = "private key type not recognised\n";
             goto error;
         }
 
@@ -1675,7 +1665,7 @@ struct ssh2_userkey *openssh_new_read(const Filename *filename,
         /*
          * Skip over the pieces of key.
          */
-        for (i = 0; i < npieces; i++) {
+        for (i = 0; i < alg->openssh_private_npieces; i++) {
             if (!(string = get_ssh_string(&privlen, &priv, &stringlen))) {
                 errmsg = "ran out of data in mid-private-key";
                 goto error;

ssh.h

@@ -333,6 +333,15 @@ struct ssh_signkey {
 			unsigned char *priv_blob, int priv_len);
     void *(*openssh_createkey) (unsigned char **blob, int *len);
     int (*openssh_fmtkey) (void *key, unsigned char *blob, int len);
+    /* OpenSSH private key blobs, as created by openssh_fmtkey and
+     * consumed by openssh_createkey, always (at least so far...) take
+     * the form of a number of SSH-2 strings / mpints concatenated
+     * end-to-end. Because the new-style OpenSSH private key format
+     * stores those blobs without a containing string wrapper, we need
+     * to know how many strings each one consists of, so that we can
+     * skip over the right number to find the next key in the file.
+     * openssh_private_npieces gives that information. */
+    int openssh_private_npieces;
     int (*pubkey_bits) (void *blob, int len);
     char *(*fingerprint) (void *key);
     int (*verifysig) (void *key, char *sig, int siglen,

sshdss.c

@@ -701,6 +701,7 @@ const struct ssh_signkey ssh_dss = {
     dss_createkey,
     dss_openssh_createkey,
     dss_openssh_fmtkey,
+    5 /* p,q,g,y,x */,
     dss_pubkey_bits,
     dss_fingerprint,
     dss_verifysig,

sshecc.c

@@ -1966,6 +1966,7 @@ const struct ssh_signkey ssh_ecdsa_nistp256 = {
     ecdsa_createkey,
     ecdsa_openssh_createkey,
     ecdsa_openssh_fmtkey,
+    3 /* curve name, point, private exponent */,
     ecdsa_pubkey_bits,
     ecdsa_fingerprint,
     ecdsa_verifysig,
@@ -1983,6 +1984,7 @@ const struct ssh_signkey ssh_ecdsa_nistp384 = {
     ecdsa_createkey,
     ecdsa_openssh_createkey,
     ecdsa_openssh_fmtkey,
+    3 /* curve name, point, private exponent */,
     ecdsa_pubkey_bits,
     ecdsa_fingerprint,
     ecdsa_verifysig,
@@ -2000,6 +2002,7 @@ const struct ssh_signkey ssh_ecdsa_nistp521 = {
     ecdsa_createkey,
     ecdsa_openssh_createkey,
     ecdsa_openssh_fmtkey,
+    3 /* curve name, point, private exponent */,
     ecdsa_pubkey_bits,
     ecdsa_fingerprint,
     ecdsa_verifysig,

sshrsa.c

@@ -942,6 +942,7 @@ const struct ssh_signkey ssh_rsa = {
     rsa2_createkey,
     rsa2_openssh_createkey,
     rsa2_openssh_fmtkey,
+    6 /* n,e,d,iqmp,q,p */,
     rsa2_pubkey_bits,
     rsa2_fingerprint,
     rsa2_verifysig,