new cipher framework

1 files changed, 296 insertions, 310 deletions

diff --git a/usr.bin/ssh/cipher.c b/usr.bin/ssh/cipher.c
index c7985a79c0c..8edb4fd42ad 100644
--- a/usr.bin/ssh/cipher.c
+++ b/usr.bin/ssh/cipher.c
@@ -35,14 +35,85 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: cipher.c,v 1.31 2000/09/12 00:38:32 deraadt Exp $");
+RCSID("$OpenBSD: cipher.c,v 1.32 2000/10/11 20:27:23 markus Exp $");
 
 #include "ssh.h"
-#include "cipher.h"
 #include "xmalloc.h"
 
 #include <openssl/md5.h>
 
+
+/* no encryption */
+void
+none_setkey(CipherContext *cc, const u_char *key, u_int keylen)
+{
+}
+void
+none_setiv(CipherContext *cc, const u_char *iv, u_int ivlen)
+{
+}
+void
+none_crypt(CipherContext *cc, u_char *dest, const u_char *src, u_int len)
+{
+	memcpy(dest, src, len);
+}
+
+/* DES */
+void
+des_ssh1_setkey(CipherContext *cc, const u_char *key, u_int keylen)
+{
+	des_set_key((void *)key, cc->u.des.key);
+}
+void
+des_ssh1_setiv(CipherContext *cc, const u_char *iv, u_int ivlen)
+{
+	memset(cc->u.des.iv, 0, sizeof(cc->u.des.iv));
+}
+void
+des_ssh1_encrypt(CipherContext *cc, u_char *dest, const u_char *src, u_int len)
+{
+	des_ncbc_encrypt(src, dest, len, cc->u.des.key, &cc->u.des.iv,
+	    DES_ENCRYPT);
+}
+void
+des_ssh1_decrypt(CipherContext *cc, u_char *dest, const u_char *src, u_int len)
+{
+	des_ncbc_encrypt(src, dest, len, cc->u.des.key, &cc->u.des.iv,
+	    DES_DECRYPT);
+}
+
+/* 3DES */
+void
+des3_setkey(CipherContext *cc, const u_char *key, u_int keylen)
+{
+	des_set_key((void *) key, cc->u.des3.key1);
+	des_set_key((void *) (key+8), cc->u.des3.key2);
+	des_set_key((void *) (key+16), cc->u.des3.key3);
+}
+void
+des3_setiv(CipherContext *cc, const u_char *iv, u_int ivlen)
+{
+	memset(cc->u.des3.iv2, 0, sizeof(cc->u.des3.iv2));
+	memset(cc->u.des3.iv3, 0, sizeof(cc->u.des3.iv3));
+	if (iv == NULL)
+		return;
+	memcpy(cc->u.des3.iv3, (char *)iv, 8);
+}
+void
+des3_cbc_encrypt(CipherContext *cc, u_char *dest, const u_char *src, u_int len)
+{
+	des_ede3_cbc_encrypt(src, dest, len,
+	    cc->u.des3.key1, cc->u.des3.key2, cc->u.des3.key3,
+	    &cc->u.des3.iv3, DES_ENCRYPT);
+}
+void
+des3_cbc_decrypt(CipherContext *cc, u_char *dest, const u_char *src, u_int len)
+{
+	des_ede3_cbc_encrypt(src, dest, len,
+	    cc->u.des3.key1, cc->u.des3.key2, cc->u.des3.key3,
+	    &cc->u.des3.iv3, DES_DECRYPT);
+}
+
 /*
  * This is used by SSH1:
  *
@@ -58,48 +129,84 @@ RCSID("$OpenBSD: cipher.c,v 1.31 2000/09/12 00:38:32 deraadt Exp $");
  * choosing the X block.
  */
 void
-SSH_3CBC_ENCRYPT(des_key_schedule ks1,
-		 des_key_schedule ks2, des_cblock * iv2,
-		 des_key_schedule ks3, des_cblock * iv3,
-		 unsigned char *dest, unsigned char *src,
-		 unsigned int len)
+des3_ssh1_setkey(CipherContext *cc, const u_char *key, u_int keylen)
+{
+	des_set_key((void *) key, cc->u.des3.key1);
+	des_set_key((void *) (key+8), cc->u.des3.key2);
+	if (keylen <= 16)
+		des_set_key((void *) key, cc->u.des3.key3);
+	else
+		des_set_key((void *) (key+16), cc->u.des3.key3);
+}
+void
+des3_ssh1_encrypt(CipherContext *cc, u_char *dest, const u_char *src,
+    u_int len)
 {
 	des_cblock iv1;
+	des_cblock *iv2 = &cc->u.des3.iv2;
+	des_cblock *iv3 = &cc->u.des3.iv3;
 
 	memcpy(&iv1, iv2, 8);
 
-	des_cbc_encrypt(src, dest, len, ks1, &iv1, DES_ENCRYPT);
+	des_cbc_encrypt(src, dest, len, cc->u.des3.key1, &iv1, DES_ENCRYPT);
 	memcpy(&iv1, dest + len - 8, 8);
 
-	des_cbc_encrypt(dest, dest, len, ks2, iv2, DES_DECRYPT);
+	des_cbc_encrypt(dest, dest, len, cc->u.des3.key2, iv2, DES_DECRYPT);
 	memcpy(iv2, &iv1, 8);	/* Note how iv1 == iv2 on entry and exit. */
 
-	des_cbc_encrypt(dest, dest, len, ks3, iv3, DES_ENCRYPT);
+	des_cbc_encrypt(dest, dest, len, cc->u.des3.key3, iv3, DES_ENCRYPT);
 	memcpy(iv3, dest + len - 8, 8);
 }
-
 void
-SSH_3CBC_DECRYPT(des_key_schedule ks1,
-		 des_key_schedule ks2, des_cblock * iv2,
-		 des_key_schedule ks3, des_cblock * iv3,
-		 unsigned char *dest, unsigned char *src,
-		 unsigned int len)
+des3_ssh1_decrypt(CipherContext *cc, u_char *dest, const u_char *src,
+    u_int len)
 {
 	des_cblock iv1;
+	des_cblock *iv2 = &cc->u.des3.iv2;
+	des_cblock *iv3 = &cc->u.des3.iv3;
 
 	memcpy(&iv1, iv2, 8);
 
-	des_cbc_encrypt(src, dest, len, ks3, iv3, DES_DECRYPT);
+	des_cbc_encrypt(src, dest, len, cc->u.des3.key3, iv3, DES_DECRYPT);
 	memcpy(iv3, src + len - 8, 8);
 
-	des_cbc_encrypt(dest, dest, len, ks2, iv2, DES_ENCRYPT);
+	des_cbc_encrypt(dest, dest, len, cc->u.des3.key2, iv2, DES_ENCRYPT);
 	memcpy(iv2, dest + len - 8, 8);
 
-	des_cbc_encrypt(dest, dest, len, ks1, &iv1, DES_DECRYPT);
+	des_cbc_encrypt(dest, dest, len, cc->u.des3.key1, &iv1, DES_DECRYPT);
 	/* memcpy(&iv1, iv2, 8); */
 	/* Note how iv1 == iv2 on entry and exit. */
 }
 
+/* Blowfish */
+void
+blowfish_setkey(CipherContext *cc, const u_char *key, u_int keylen)
+{
+	BF_set_key(&cc->u.bf.key, keylen, (unsigned char *)key);
+}
+void
+blowfish_setiv(CipherContext *cc, const u_char *iv, u_int ivlen)
+{
+	if (iv == NULL)
+		memset(cc->u.bf.iv, 0, 8);
+	else
+		memcpy(cc->u.bf.iv, (char *)iv, 8);
+}
+void
+blowfish_cbc_encrypt(CipherContext *cc, u_char *dest, const u_char *src,
+     u_int len)
+{
+	BF_cbc_encrypt((void *)src, dest, len, &cc->u.bf.key, cc->u.bf.iv,
+	    BF_ENCRYPT);
+}
+void
+blowfish_cbc_decrypt(CipherContext *cc, u_char *dest, const u_char *src,
+     u_int len)
+{
+	BF_cbc_encrypt((void *)src, dest, len, &cc->u.bf.key, cc->u.bf.iv,
+	    BF_DECRYPT);
+}
+
 /*
  * SSH1 uses a variation on Blowfish, all bytes must be swapped before
  * and after encryption/decryption. Thus the swap_bytes stuff (yuk).
@@ -130,88 +237,162 @@ swap_bytes(const unsigned char *src, unsigned char *dst_, int n)
 	}
 }
 
-/*
- * Names of all encryption algorithms.
- * These must match the numbers defined in cipher.h.
- */
-static char *cipher_names[] =
-{
-	"none",
-	"idea",
-	"des",
-	"3des",
-	"tss",
-	"rc4",		/* Alleged RC4 */
-	"blowfish",
-	"reserved",
-	"blowfish-cbc",
-	"3des-cbc",
-	"arcfour",
-	"cast128-cbc"
-};
+void
+blowfish_ssh1_encrypt(CipherContext *cc, u_char *dest, const u_char *src,
+    u_int len)
+{
+	swap_bytes(src, dest, len);
+	BF_cbc_encrypt((void *)dest, dest, len, &cc->u.bf.key, cc->u.bf.iv,
+	    BF_ENCRYPT);
+	swap_bytes(dest, dest, len);
+}
+void
+blowfish_ssh1_decrypt(CipherContext *cc, u_char *dest, const u_char *src,
+    u_int len)
+{
+	swap_bytes(src, dest, len);
+	BF_cbc_encrypt((void *)dest, dest, len, &cc->u.bf.key, cc->u.bf.iv,
+	    BF_DECRYPT);
+	swap_bytes(dest, dest, len);
+}
 
-/*
- * Returns a bit mask indicating which ciphers are supported by this
- * implementation.  The bit mask has the corresponding bit set of each
- * supported cipher.
- */
+/* alleged rc4 */
+void
+arcfour_setkey(CipherContext *cc, const u_char *key, u_int keylen)
+{
+	RC4_set_key(&cc->u.rc4, keylen, (u_char *)key);
+}
+void
+arcfour_crypt(CipherContext *cc, u_char *dest, const u_char *src, u_int len)
+{
+	RC4(&cc->u.rc4, len, (u_char *)src, dest);
+}
 
-unsigned int
-cipher_mask1()
+/* CAST */
+void
+cast_setkey(CipherContext *cc, const u_char *key, u_int keylen)
 {
-	unsigned int mask = 0;
-	mask |= 1 << SSH_CIPHER_3DES;		/* Mandatory */
-	mask |= 1 << SSH_CIPHER_BLOWFISH;
-	return mask;
+	CAST_set_key(&cc->u.cast.key, keylen, (unsigned char *) key);
+}
+void
+cast_setiv(CipherContext *cc, const u_char *iv, u_int ivlen)
+{
+	if (iv == NULL) 
+		fatal("no IV for %s.", cc->cipher->name);
+	memcpy(cc->u.cast.iv, (char *)iv, 8);
+}
+void
+cast_cbc_encrypt(CipherContext *cc, u_char *dest, const u_char *src, u_int len)
+{
+	CAST_cbc_encrypt(src, dest, len, &cc->u.cast.key, cc->u.cast.iv,
+	    CAST_ENCRYPT);
+}
+void
+cast_cbc_decrypt(CipherContext *cc, u_char *dest, const u_char *src, u_int len)
+{
+	CAST_cbc_encrypt(src, dest, len, &cc->u.cast.key, cc->u.cast.iv,
+	    CAST_DECRYPT);
 }
+
+/*--*/
+
+Cipher ciphers[] = {
+	{ "none",
+		SSH_CIPHER_NONE, 8, 0,
+		none_setkey, none_setiv,
+		none_crypt, none_crypt },
+	{ "des",
+		SSH_CIPHER_DES, 8, 8,
+		des_ssh1_setkey, des_ssh1_setiv,
+		des_ssh1_encrypt, des_ssh1_decrypt },
+	{ "3des",
+		SSH_CIPHER_3DES, 8, 16,
+		des3_ssh1_setkey, des3_setiv,
+		des3_ssh1_encrypt, des3_ssh1_decrypt },
+	{ "blowfish",
+		SSH_CIPHER_BLOWFISH, 8, 16,
+		blowfish_setkey, blowfish_setiv,
+		blowfish_ssh1_encrypt, blowfish_ssh1_decrypt },
+
+	{ "3des-cbc",
+		SSH_CIPHER_SSH2, 8, 24,
+		des3_setkey, des3_setiv,
+		des3_cbc_encrypt, des3_cbc_decrypt },
+	{ "blowfish-cbc",
+		SSH_CIPHER_SSH2, 8, 16,
+		blowfish_setkey, blowfish_setiv,
+		blowfish_cbc_encrypt, blowfish_cbc_decrypt },
+	{ "cast128-cbc",
+		SSH_CIPHER_SSH2, 8, 16,
+		cast_setkey, cast_setiv,
+		cast_cbc_encrypt, cast_cbc_decrypt },
+	{ "arcfour",
+		SSH_CIPHER_SSH2, 8, 16,
+		arcfour_setkey, none_setiv,
+		arcfour_crypt, arcfour_crypt },
+        { NULL, SSH_CIPHER_ILLEGAL, 0, 0, NULL, NULL, NULL, NULL }
+};
+
+/*--*/
+
 unsigned int
-cipher_mask2()
+cipher_mask1()
 {
 	unsigned int mask = 0;
-	mask |= 1 << SSH_CIPHER_BLOWFISH_CBC;
-	mask |= 1 << SSH_CIPHER_3DES_CBC;
-	mask |= 1 << SSH_CIPHER_ARCFOUR;
-	mask |= 1 << SSH_CIPHER_CAST128_CBC;
+	Cipher *c;
+	for (c = ciphers; c->name != NULL; c++) {
+		if (c->number > SSH_CIPHER_NONE)
+			mask |= 1 << c->number;
+	}
 	return mask;
 }
-unsigned int
-cipher_mask()
+
+Cipher *
+cipher_by_name(const char *name)
 {
-	return cipher_mask1() | cipher_mask2();
+	Cipher *c;
+	if (strcmp(name, "des") == 0)
+		error("Warning: use of DES is strongly discouraged "
+		    "due to cryptographic weaknesses");
+	for (c = ciphers; c->name != NULL; c++)
+		if (strcasecmp(c->name, name) == 0)
+			return c;
+	return NULL;
 }
 
-/* Returns the name of the cipher. */
-
-const char *
-cipher_name(int cipher)
+Cipher *
+cipher_by_number(int id)
 {
-	if (cipher < 0 || cipher >= sizeof(cipher_names) / sizeof(cipher_names[0]) ||
-	    cipher_names[cipher] == NULL)
-		fatal("cipher_name: bad cipher name: %d", cipher);
-	return cipher_names[cipher];
+	Cipher *c;
+	for (c = ciphers; c->name != NULL; c++)
+		if (c->number == id)
+			return c;
+	return NULL;
 }
 
-/* Returns 1 if the name of the ciphers are valid. */
-
 #define	CIPHER_SEP	","
 int
 ciphers_valid(const char *names)
 {
+	Cipher *c;
 	char *ciphers, *cp;
 	char *p;
-	int i;
 
 	if (names == NULL || strcmp(names, "") == 0)
 		return 0;
 	ciphers = cp = xstrdup(names);
-	for ((p = strsep(&cp, CIPHER_SEP)); p && *p != '\0'; 
+	for ((p = strsep(&cp, CIPHER_SEP)); p && *p != '\0';
 	     (p = strsep(&cp, CIPHER_SEP))) {
-		i = cipher_number(p);
-		if (i == -1 || !(cipher_mask2() & (1 << i))) {
+		c = cipher_by_name(p);
+		if (c == NULL || c->number != SSH_CIPHER_SSH2) {
+			debug("bad cipher %s [%s]", p, names);
 			xfree(ciphers);
 			return 0;
+		} else {
+			debug("cipher ok: %s [%s]", p, names);
 		}
 	}
+	debug("ciphers ok: [%s]", names);
 	xfree(ciphers);
 	return 1;
 }
@@ -224,264 +405,69 @@ ciphers_valid(const char *names)
 int
 cipher_number(const char *name)
 {
-	int i;
+	Cipher *c;
 	if (name == NULL)
 		return -1;
-	for (i = 0; i < sizeof(cipher_names) / sizeof(cipher_names[0]); i++)
-		if (strcmp(cipher_names[i], name) == 0 &&
-		    (cipher_mask() & (1 << i)))
-			return i;
-	return -1;
+	c = cipher_by_name(name);
+	return (c==NULL) ? -1 : c->number;
 }
 
-/*
- * Selects the cipher, and keys if by computing the MD5 checksum of the
- * passphrase and using the resulting 16 bytes as the key.
- */
-
-void
-cipher_set_key_string(CipherContext *context, int cipher, const char *passphrase)
+char *
+cipher_name(int id)
 {
-	MD5_CTX md;
-	unsigned char digest[16];
-
-	MD5_Init(&md);
-	MD5_Update(&md, (const unsigned char *) passphrase, strlen(passphrase));
-	MD5_Final(digest, &md);
-
-	cipher_set_key(context, cipher, digest, 16);
-
-	memset(digest, 0, sizeof(digest));
-	memset(&md, 0, sizeof(md));
+	Cipher *c = cipher_by_number(id);
+	return (c==NULL) ? "<unknown>" : c->name;
 }
 
-/* Selects the cipher to use and sets the key. */
-
 void
-cipher_set_key(CipherContext *context, int cipher, const unsigned char *key,
-    int keylen)
-{
-	unsigned char padded[32];
-
-	/* Set cipher type. */
-	context->type = cipher;
-
-	/* Get 32 bytes of key data.  Pad if necessary.  (So that code
-	   below does not need to worry about key size). */
-	memset(padded, 0, sizeof(padded));
-	memcpy(padded, key, keylen < sizeof(padded) ? keylen : sizeof(padded));
-
-	/* Initialize the initialization vector. */
-	switch (cipher) {
-	case SSH_CIPHER_NONE:
-		/*
-		 * Has to stay for authfile saving of private key with no
-		 * passphrase
-		 */
-		break;
-
-	case SSH_CIPHER_3DES:
-		/*
-		 * Note: the least significant bit of each byte of key is
-		 * parity, and must be ignored by the implementation.  16
-		 * bytes of key are used (first and last keys are the same).
-		 */
-		if (keylen < 16)
-			error("Key length %d is insufficient for 3DES.", keylen);
-		des_set_key((void *) padded, context->u.des3.key1);
-		des_set_key((void *) (padded + 8), context->u.des3.key2);
-		if (keylen <= 16)
-			des_set_key((void *) padded, context->u.des3.key3);
-		else
-			des_set_key((void *) (padded + 16), context->u.des3.key3);
-		memset(context->u.des3.iv2, 0, sizeof(context->u.des3.iv2));
-		memset(context->u.des3.iv3, 0, sizeof(context->u.des3.iv3));
-		break;
-
-	case SSH_CIPHER_BLOWFISH:
-		if (keylen < 16)
-			error("Key length %d is insufficient for blowfish.", keylen);
-		BF_set_key(&context->u.bf.key, keylen, padded);
-		memset(context->u.bf.iv, 0, 8);
-		break;
-
-	case SSH_CIPHER_3DES_CBC:
-	case SSH_CIPHER_BLOWFISH_CBC:
-	case SSH_CIPHER_ARCFOUR:
-	case SSH_CIPHER_CAST128_CBC:
-		fatal("cipher_set_key: illegal cipher: %s", cipher_name(cipher));
-		break;
-
-	default:
-		fatal("cipher_set_key: unknown cipher: %s", cipher_name(cipher));
-	}
-	memset(padded, 0, sizeof(padded));
+cipher_init(CipherContext *cc, Cipher *cipher,
+    const u_char *key, u_int keylen, const u_char *iv, u_int ivlen)
+{
+	if (keylen < cipher->key_len)
+		fatal("cipher_init: key length %d is insufficient for %s.",
+		    keylen, cipher->name);
+	if (iv != NULL && ivlen < cipher->block_size)
+		fatal("cipher_init: iv length %d is insufficient for %s.",
+		    ivlen, cipher->name);
+	cc->cipher = cipher;
+	cipher->setkey(cc, key, keylen);
+	cipher->setiv(cc, iv, ivlen);
 }
 
 void
-cipher_set_key_iv(CipherContext * context, int cipher,
-    const unsigned char *key, int keylen,
-    const unsigned char *iv, int ivlen)
-{
-	/* Set cipher type. */
-	context->type = cipher;
-
-	/* Initialize the initialization vector. */
-	switch (cipher) {
-	case SSH_CIPHER_NONE:
-		break;
-
-	case SSH_CIPHER_3DES:
-	case SSH_CIPHER_BLOWFISH:
-		fatal("cipher_set_key_iv: illegal cipher: %s", cipher_name(cipher));
-		break;
-
-	case SSH_CIPHER_3DES_CBC:
-		if (keylen < 24)
-			error("Key length %d is insufficient for 3des-cbc.", keylen);
-		des_set_key((void *) key, context->u.des3.key1);
-		des_set_key((void *) (key+8), context->u.des3.key2);
-		des_set_key((void *) (key+16), context->u.des3.key3);
-		if (ivlen < 8)
-			error("IV length %d is insufficient for 3des-cbc.", ivlen);
-		memcpy(context->u.des3.iv3, (char *)iv, 8);
-		break;
-
-	case SSH_CIPHER_BLOWFISH_CBC:
-		if (keylen < 16)
-			error("Key length %d is insufficient for blowfish.", keylen);
-		if (ivlen < 8)
-			error("IV length %d is insufficient for blowfish.", ivlen);
-		BF_set_key(&context->u.bf.key, keylen, (unsigned char *)key);
-		memcpy(context->u.bf.iv, (char *)iv, 8);
-		break;
-
-	case SSH_CIPHER_ARCFOUR:
-		if (keylen < 16)
-			error("Key length %d is insufficient for arcfour.", keylen);
-		RC4_set_key(&context->u.rc4, keylen, (unsigned char *)key);
-		break;
-
-	case SSH_CIPHER_CAST128_CBC:
-		if (keylen < 16)
-			error("Key length %d is insufficient for cast128.", keylen);
-		if (ivlen < 8)
-			error("IV length %d is insufficient for cast128.", ivlen);
-		CAST_set_key(&context->u.cast.key, keylen, (unsigned char *) key);
-		memcpy(context->u.cast.iv, (char *)iv, 8);
-		break;
-
-	default:
-		fatal("cipher_set_key: unknown cipher: %s", cipher_name(cipher));
-	}
+cipher_encrypt(CipherContext *cc, u_char *dest, const u_char *src, u_int len)
+{
+	if (len % cc->cipher->block_size)
+		fatal("cipher_encrypt: bad plaintext length %d", len);
+	cc->cipher->encrypt(cc, dest, src, len);
 }
 
-/* Encrypts data using the cipher. */
-
 void
-cipher_encrypt(CipherContext *context, unsigned char *dest,
-	       const unsigned char *src, unsigned int len)
+cipher_decrypt(CipherContext *cc, u_char *dest, const u_char *src, u_int len)
 {
-	if ((len & 7) != 0)
-		fatal("cipher_encrypt: bad plaintext length %d", len);
-
-	switch (context->type) {
-	case SSH_CIPHER_NONE:
-		memcpy(dest, src, len);
-		break;
-
-	case SSH_CIPHER_3DES:
-		SSH_3CBC_ENCRYPT(context->u.des3.key1,
-				 context->u.des3.key2, &context->u.des3.iv2,
-				 context->u.des3.key3, &context->u.des3.iv3,
-				 dest, (unsigned char *) src, len);
-		break;
-
-	case SSH_CIPHER_BLOWFISH:
-		swap_bytes(src, dest, len);
-		BF_cbc_encrypt(dest, dest, len,
-			       &context->u.bf.key, context->u.bf.iv,
-			       BF_ENCRYPT);
-		swap_bytes(dest, dest, len);
-		break;
-
-	case SSH_CIPHER_BLOWFISH_CBC:
-		BF_cbc_encrypt((void *)src, dest, len,
-			       &context->u.bf.key, context->u.bf.iv,
-			       BF_ENCRYPT);
-		break;
-
-	case SSH_CIPHER_3DES_CBC:
-		des_ede3_cbc_encrypt(src, dest, len,
-		    context->u.des3.key1, context->u.des3.key2,
-		    context->u.des3.key3, &context->u.des3.iv3, DES_ENCRYPT);
-		break;
-
-	case SSH_CIPHER_ARCFOUR:
-		RC4(&context->u.rc4, len, (unsigned char *)src, dest);
-		break;
-
-	case SSH_CIPHER_CAST128_CBC:
-		CAST_cbc_encrypt(src, dest, len,
-		    &context->u.cast.key, context->u.cast.iv, CAST_ENCRYPT);
-		break;
-
-	default:
-		fatal("cipher_encrypt: unknown cipher: %s", cipher_name(context->type));
-	}
+	if (len % cc->cipher->block_size)
+		fatal("cipher_decrypt: bad ciphertext length %d", len);
+	cc->cipher->decrypt(cc, dest, src, len);
 }
 
-/* Decrypts data using the cipher. */
+/*
+ * Selects the cipher, and keys if by computing the MD5 checksum of the
+ * passphrase and using the resulting 16 bytes as the key.
+ */
 
 void
-cipher_decrypt(CipherContext *context, unsigned char *dest,
-	       const unsigned char *src, unsigned int len)
+cipher_set_key_string(CipherContext *cc, Cipher *cipher,
+    const char *passphrase)
 {
-	if ((len & 7) != 0)
-		fatal("cipher_decrypt: bad ciphertext length %d", len);
+	MD5_CTX md;
+	unsigned char digest[16];
 
-	switch (context->type) {
-	case SSH_CIPHER_NONE:
-		memcpy(dest, src, len);
-		break;
-
-	case SSH_CIPHER_3DES:
-		SSH_3CBC_DECRYPT(context->u.des3.key1,
-				 context->u.des3.key2, &context->u.des3.iv2,
-				 context->u.des3.key3, &context->u.des3.iv3,
-				 dest, (unsigned char *) src, len);
-		break;
-
-	case SSH_CIPHER_BLOWFISH:
-		swap_bytes(src, dest, len);
-		BF_cbc_encrypt((void *) dest, dest, len,
-			       &context->u.bf.key, context->u.bf.iv,
-			       BF_DECRYPT);
-		swap_bytes(dest, dest, len);
-		break;
-
-	case SSH_CIPHER_BLOWFISH_CBC:
-		BF_cbc_encrypt((void *) src, dest, len,
-			       &context->u.bf.key, context->u.bf.iv,
-			       BF_DECRYPT);
-		break;
-
-	case SSH_CIPHER_3DES_CBC:
-		des_ede3_cbc_encrypt(src, dest, len,
-		    context->u.des3.key1, context->u.des3.key2,
-		    context->u.des3.key3, &context->u.des3.iv3, DES_DECRYPT);
-		break;
-
-	case SSH_CIPHER_ARCFOUR:
-		RC4(&context->u.rc4, len, (unsigned char *)src, dest);
-		break;
-
-	case SSH_CIPHER_CAST128_CBC:
-		CAST_cbc_encrypt(src, dest, len,
-		    &context->u.cast.key, context->u.cast.iv, CAST_DECRYPT);
-		break;
-
-	default:
-		fatal("cipher_decrypt: unknown cipher: %s", cipher_name(context->type));
-	}
+	MD5_Init(&md);
+	MD5_Update(&md, (const u_char *)passphrase, strlen(passphrase));
+	MD5_Final(digest, &md);
+
+	cipher_init(cc, cipher, digest, 16, NULL, 0);
+
+	memset(digest, 0, sizeof(digest));
+	memset(&md, 0, sizeof(md));
 }