diff --git a/ssh.c b/ssh.c
index f56e10a9..4979268f 100644
--- a/ssh.c
+++ b/ssh.c
@@ -6728,8 +6728,8 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
         {
             int csbits, scbits;
 
-            csbits = s->cscipher_tobe->keylen;
-            scbits = s->sccipher_tobe->keylen;
+            csbits = s->cscipher_tobe->real_keybits;
+            scbits = s->sccipher_tobe->real_keybits;
             s->nbits = (csbits > scbits ? csbits : scbits);
         }
         /* The keys only have hlen-bit entropy, since they're based on
@@ -7183,9 +7183,9 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
 	unsigned char *key;
 
 	key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'C',
-                         (ssh->cscipher->keylen+7) / 8);
+                         ssh->cscipher->padded_keybytes);
 	ssh->cscipher->setkey(ssh->cs_cipher_ctx, key);
-        smemclr(key, (ssh->cscipher->keylen+7) / 8);
+        smemclr(key, ssh->cscipher->padded_keybytes);
         sfree(key);
 
 	key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'A',
@@ -7256,9 +7256,9 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
 	unsigned char *key;
 
 	key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'D',
-                         (ssh->sccipher->keylen + 7) / 8);
+                         ssh->sccipher->padded_keybytes);
 	ssh->sccipher->setkey(ssh->sc_cipher_ctx, key);
-        smemclr(key, (ssh->sccipher->keylen + 7) / 8);
+        smemclr(key, ssh->sccipher->padded_keybytes);
         sfree(key);
 
 	key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'B',
diff --git a/ssh.h b/ssh.h
index ef488e83..e8f1adad 100644
--- a/ssh.h
+++ b/ssh.h
@@ -319,7 +319,19 @@ struct ssh2_cipher {
     void (*decrypt_length) (void *, unsigned char *blk, int len, unsigned long seq);
     const char *name;
     int blksize;
-    int keylen;
+    /* real_keybits is the number of bits of entropy genuinely used by
+     * the cipher scheme; it's used for deciding how big a
+     * Diffie-Hellman group is needed to exchange a key for the
+     * cipher. */
+    int real_keybits;
+    /* padded_keybytes is the number of bytes of key data expected as
+     * input to the setkey function; it's used for deciding how much
+     * data needs to be generated from the post-kex generation of key
+     * material. In a sensible cipher which uses all its key bytes for
+     * real work, this will just be real_keybits/8, but in DES-type
+     * ciphers which ignore one bit in each byte, it'll be slightly
+     * different. */
+    int padded_keybytes;
     unsigned int flags;
 #define SSH_CIPHER_IS_CBC	1
 #define SSH_CIPHER_SEPARATE_LENGTH      2
diff --git a/sshaes.c b/sshaes.c
index 0465d879..904cbdb2 100644
--- a/sshaes.c
+++ b/sshaes.c
@@ -1173,7 +1173,7 @@ static const struct ssh2_cipher ssh_aes128_ctr = {
     aes_make_context, aes_free_context, aes_iv, aes128_key,
     aes_ssh2_sdctr, aes_ssh2_sdctr, NULL, NULL,
     "aes128-ctr",
-    16, 128, 0, "AES-128 SDCTR",
+    16, 128, 16, 0, "AES-128 SDCTR",
     NULL
 };
 
@@ -1181,7 +1181,7 @@ static const struct ssh2_cipher ssh_aes192_ctr = {
     aes_make_context, aes_free_context, aes_iv, aes192_key,
     aes_ssh2_sdctr, aes_ssh2_sdctr, NULL, NULL,
     "aes192-ctr",
-    16, 192, 0, "AES-192 SDCTR",
+    16, 192, 24, 0, "AES-192 SDCTR",
     NULL
 };
 
@@ -1189,7 +1189,7 @@ static const struct ssh2_cipher ssh_aes256_ctr = {
     aes_make_context, aes_free_context, aes_iv, aes256_key,
     aes_ssh2_sdctr, aes_ssh2_sdctr, NULL, NULL,
     "aes256-ctr",
-    16, 256, 0, "AES-256 SDCTR",
+    16, 256, 32, 0, "AES-256 SDCTR",
     NULL
 };
 
@@ -1197,7 +1197,7 @@ static const struct ssh2_cipher ssh_aes128 = {
     aes_make_context, aes_free_context, aes_iv, aes128_key,
     aes_ssh2_encrypt_blk, aes_ssh2_decrypt_blk, NULL, NULL,
     "aes128-cbc",
-    16, 128, SSH_CIPHER_IS_CBC, "AES-128 CBC",
+    16, 128, 16, SSH_CIPHER_IS_CBC, "AES-128 CBC",
     NULL
 };
 
@@ -1205,7 +1205,7 @@ static const struct ssh2_cipher ssh_aes192 = {
     aes_make_context, aes_free_context, aes_iv, aes192_key,
     aes_ssh2_encrypt_blk, aes_ssh2_decrypt_blk, NULL, NULL,
     "aes192-cbc",
-    16, 192, SSH_CIPHER_IS_CBC, "AES-192 CBC",
+    16, 192, 24, SSH_CIPHER_IS_CBC, "AES-192 CBC",
     NULL
 };
 
@@ -1213,7 +1213,7 @@ static const struct ssh2_cipher ssh_aes256 = {
     aes_make_context, aes_free_context, aes_iv, aes256_key,
     aes_ssh2_encrypt_blk, aes_ssh2_decrypt_blk, NULL, NULL,
     "aes256-cbc",
-    16, 256, SSH_CIPHER_IS_CBC, "AES-256 CBC",
+    16, 256, 32, SSH_CIPHER_IS_CBC, "AES-256 CBC",
     NULL
 };
 
@@ -1221,7 +1221,7 @@ static const struct ssh2_cipher ssh_rijndael_lysator = {
     aes_make_context, aes_free_context, aes_iv, aes256_key,
     aes_ssh2_encrypt_blk, aes_ssh2_decrypt_blk, NULL, NULL,
     "rijndael-cbc@lysator.liu.se",
-    16, 256, SSH_CIPHER_IS_CBC, "AES-256 CBC",
+    16, 256, 32, SSH_CIPHER_IS_CBC, "AES-256 CBC",
     NULL
 };
 
diff --git a/ssharcf.c b/ssharcf.c
index a9d5f7da..d16ce225 100644
--- a/ssharcf.c
+++ b/ssharcf.c
@@ -102,7 +102,7 @@ const struct ssh2_cipher ssh_arcfour128_ssh2 = {
     arcfour_make_context, arcfour_free_context, arcfour_iv, arcfour128_key,
     arcfour_block, arcfour_block, NULL, NULL,
     "arcfour128",
-    1, 128, 0, "Arcfour-128",
+    1, 128, 16, 0, "Arcfour-128",
     NULL
 };
 
@@ -110,7 +110,7 @@ const struct ssh2_cipher ssh_arcfour256_ssh2 = {
     arcfour_make_context, arcfour_free_context, arcfour_iv, arcfour256_key,
     arcfour_block, arcfour_block, NULL, NULL,
     "arcfour256",
-    1, 256, 0, "Arcfour-256",
+    1, 256, 32, 0, "Arcfour-256",
     NULL
 };
 
diff --git a/sshblowf.c b/sshblowf.c
index 8a561b37..353116a6 100644
--- a/sshblowf.c
+++ b/sshblowf.c
@@ -643,7 +643,7 @@ static const struct ssh2_cipher ssh_blowfish_ssh2 = {
     blowfish_make_context, blowfish_free_context, blowfish_iv, blowfish_key,
     blowfish_ssh2_encrypt_blk, blowfish_ssh2_decrypt_blk, NULL, NULL,
     "blowfish-cbc",
-    8, 128, SSH_CIPHER_IS_CBC, "Blowfish-128 CBC",
+    8, 128, 16, SSH_CIPHER_IS_CBC, "Blowfish-128 CBC",
     NULL
 };
 
@@ -651,7 +651,7 @@ static const struct ssh2_cipher ssh_blowfish_ssh2_ctr = {
     blowfish_make_context, blowfish_free_context, blowfish_iv, blowfish256_key,
     blowfish_ssh2_sdctr, blowfish_ssh2_sdctr, NULL, NULL,
     "blowfish-ctr",
-    8, 256, 0, "Blowfish-256 SDCTR",
+    8, 256, 32, 0, "Blowfish-256 SDCTR",
     NULL
 };
 
diff --git a/sshccp.c b/sshccp.c
index 5400d36c..0b3dc573 100644
--- a/sshccp.c
+++ b/sshccp.c
@@ -1331,7 +1331,7 @@ static const struct ssh2_cipher ssh2_chacha20_poly1305 = {
     ccp_decrypt_length,
 
     "chacha20-poly1305@openssh.com",
-    1, 512, SSH_CIPHER_SEPARATE_LENGTH, "ChaCha20",
+    1, 512, 64, SSH_CIPHER_SEPARATE_LENGTH, "ChaCha20",
 
     &ssh2_poly1305
 };
diff --git a/sshdes.c b/sshdes.c
index 9276fe06..13487fcd 100644
--- a/sshdes.c
+++ b/sshdes.c
@@ -949,7 +949,7 @@ static const struct ssh2_cipher ssh_3des_ssh2 = {
     des3_make_context, des3_free_context, des3_iv, des3_key,
     des3_ssh2_encrypt_blk, des3_ssh2_decrypt_blk, NULL, NULL,
     "3des-cbc",
-    8, 168, SSH_CIPHER_IS_CBC, "triple-DES CBC",
+    8, 168, 24, SSH_CIPHER_IS_CBC, "triple-DES CBC",
     NULL
 };
 
@@ -957,7 +957,7 @@ static const struct ssh2_cipher ssh_3des_ssh2_ctr = {
     des3_make_context, des3_free_context, des3_iv, des3_key,
     des3_ssh2_sdctr, des3_ssh2_sdctr, NULL, NULL,
     "3des-ctr",
-    8, 168, 0, "triple-DES SDCTR",
+    8, 168, 24, 0, "triple-DES SDCTR",
     NULL
 };
 
@@ -973,7 +973,7 @@ static const struct ssh2_cipher ssh_des_ssh2 = {
     des_make_context, des3_free_context, des3_iv, des_key,
     des_ssh2_encrypt_blk, des_ssh2_decrypt_blk, NULL, NULL,
     "des-cbc",
-    8, 56, SSH_CIPHER_IS_CBC, "single-DES CBC",
+    8, 56, 8, SSH_CIPHER_IS_CBC, "single-DES CBC",
     NULL
 };
 
@@ -981,7 +981,7 @@ static const struct ssh2_cipher ssh_des_sshcom_ssh2 = {
     des_make_context, des3_free_context, des3_iv, des_key,
     des_ssh2_encrypt_blk, des_ssh2_decrypt_blk, NULL, NULL,
     "des-cbc@ssh.com",
-    8, 56, SSH_CIPHER_IS_CBC, "single-DES CBC",
+    8, 56, 8, SSH_CIPHER_IS_CBC, "single-DES CBC",
     NULL
 };