diff --git a/ssh.h b/ssh.h
index b860e7a8..e3b967fd 100644
--- a/ssh.h
+++ b/ssh.h
@@ -716,7 +716,7 @@ struct ssh2_macalg {
     /* Passes in the cipher context */
     ssh2_mac *(*new)(const struct ssh2_macalg *alg, ssh2_cipher *cipher);
     void (*free)(ssh2_mac *);
-    void (*setkey)(ssh2_mac *, const void *key);
+    void (*setkey)(ssh2_mac *, ptrlen key);
     void (*start)(ssh2_mac *);
     void (*genresult)(ssh2_mac *, unsigned char *);
     const char *name, *etm_name;
diff --git a/ssh2bpp.c b/ssh2bpp.c
index 8cb82356..1343f79b 100644
--- a/ssh2bpp.c
+++ b/ssh2bpp.c
@@ -137,7 +137,7 @@ void ssh2_bpp_new_outgoing_crypto(
     s->out.etm_mode = etm_mode;
     if (mac) {
         s->out.mac = ssh2_mac_new(mac, s->out.cipher);
-        ssh2_mac_setkey(s->out.mac, mac_key);
+        ssh2_mac_setkey(s->out.mac, make_ptrlen(mac_key, mac->keylen));
 
         bpp_logevent("Initialised %s outbound MAC algorithm%s%s",
                      ssh2_mac_alg(s->out.mac)->text_name,
@@ -194,7 +194,7 @@ void ssh2_bpp_new_incoming_crypto(
     s->in.etm_mode = etm_mode;
     if (mac) {
         s->in.mac = ssh2_mac_new(mac, s->in.cipher);
-        ssh2_mac_setkey(s->in.mac, mac_key);
+        ssh2_mac_setkey(s->in.mac, make_ptrlen(mac_key, mac->keylen));
 
         bpp_logevent("Initialised %s inbound MAC algorithm%s%s",
                      ssh2_mac_alg(s->in.mac)->text_name,
diff --git a/sshccp.c b/sshccp.c
index 81ae45b6..2a15c164 100644
--- a/sshccp.c
+++ b/sshccp.c
@@ -772,11 +772,12 @@ static void poly1305_init(struct poly1305 *ctx)
     bigval_clear(&ctx->h);
 }
 
-/* Takes a 256 bit key */
-static void poly1305_key(struct poly1305 *ctx, const unsigned char *key)
+static void poly1305_key(struct poly1305 *ctx, ptrlen key)
 {
+    assert(key.len == 32);             /* Takes a 256 bit key */
+
     unsigned char key_copy[16];
-    memcpy(key_copy, key, 16);
+    memcpy(key_copy, key.ptr, 16);
 
     /* Key the MAC itself
      * bytes 4, 8, 12 and 16 are required to have their top four bits clear */
@@ -791,8 +792,8 @@ static void poly1305_key(struct poly1305 *ctx, const unsigned char *key)
     bigval_import_le(&ctx->r, key_copy, 16);
     smemclr(key_copy, sizeof(key_copy));
 
-    /* Use second 128 bits are the nonce */
-    memcpy(ctx->nonce, key+16, 16);
+    /* Use second 128 bits as the nonce */
+    memcpy(ctx->nonce, (const char *)key.ptr + 16, 16);
 }
 
 /* Feed up to 16 bytes (should only be less for the last chunk) */
@@ -884,7 +885,7 @@ static void poly_ssh2_free(ssh2_mac *mac)
     /* Not allocated, just forwarded, no need to free */
 }
 
-static void poly_setkey(ssh2_mac *mac, const void *key)
+static void poly_setkey(ssh2_mac *mac, ptrlen key)
 {
     /* Uses the same context as ChaCha20, so ignore */
 }
@@ -919,7 +920,7 @@ static void poly_BinarySink_write(BinarySink *bs, const void *blkv, size_t len)
         chacha20_round(&ctx->b_cipher);
 
         /* Set the poly key */
-        poly1305_key(&ctx->mac, ctx->b_cipher.current);
+        poly1305_key(&ctx->mac, make_ptrlen(ctx->b_cipher.current, 32));
 
         /* Set the first round as used */
         ctx->b_cipher.currentIndex = 64;
diff --git a/sshmd5.c b/sshmd5.c
index b4121aa5..12e70b1f 100644
--- a/sshmd5.c
+++ b/sshmd5.c
@@ -273,11 +273,11 @@ void hmacmd5_key(struct hmacmd5_context *ctx, void const *keyv, int len)
     smemclr(foo, 64);		       /* burn the evidence */
 }
 
-static void hmacmd5_ssh2_setkey(ssh2_mac *mac, const void *key)
+static void hmacmd5_ssh2_setkey(ssh2_mac *mac, ptrlen key)
 {
     struct hmacmd5_context *ctx =
         container_of(mac, struct hmacmd5_context, mac);
-    hmacmd5_key(ctx, key, ctx->mac.vt->keylen);
+    hmacmd5_key(ctx, key.ptr, key.len);
 }
 
 static void hmacmd5_start(ssh2_mac *mac)
diff --git a/sshsh256.c b/sshsh256.c
index d8438e25..a3377ade 100644
--- a/sshsh256.c
+++ b/sshsh256.c
@@ -293,10 +293,10 @@ static void sha256_key_internal(struct hmacsha256 *ctx,
     smemclr(foo, 64);		       /* burn the evidence */
 }
 
-static void hmacsha256_key(ssh2_mac *mac, const void *key)
+static void hmacsha256_key(ssh2_mac *mac, ptrlen key)
 {
     struct hmacsha256 *ctx = container_of(mac, struct hmacsha256, mac);
-    sha256_key_internal(ctx, key, ctx->mac.vt->keylen);
+    sha256_key_internal(ctx, key.ptr, key.len);
 }
 
 static void hmacsha256_start(ssh2_mac *mac)
diff --git a/sshsha.c b/sshsha.c
index b49355c5..545e8c48 100644
--- a/sshsha.c
+++ b/sshsha.c
@@ -322,13 +322,10 @@ static void sha1_key_internal(SHA_State *keys,
     smemclr(foo, 64);		       /* burn the evidence */
 }
 
-static void hmacsha1_key(ssh2_mac *mac, const void *key)
+static void hmacsha1_key(ssh2_mac *mac, ptrlen key)
 {
     struct hmacsha1 *ctx = container_of(mac, struct hmacsha1, mac);
-    /* Reading the key length out of the ssh2_macalg structure means
-     * this same method can be used for the _buggy variants which use
-     * a shorter key */
-    sha1_key_internal(ctx->sha, key, ctx->mac.vt->keylen);
+    sha1_key_internal(ctx->sha, key.ptr, key.len);
 }
 
 static void hmacsha1_start(ssh2_mac *mac)