cipher.c - security/openssh-library - Rivoreo Source Code Repositories

 /*
  *
  * cipher.c
  *
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  *
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
  *                    All rights reserved
  *
  * Created: Wed Apr 19 17:41:39 1995 ylo
  *
  */

 #include "includes.h"
 RCSID("$OpenBSD: cipher.c,v 1.28 2000/06/20 01:39:40 markus Exp $");

 #include "ssh.h"
 #include "cipher.h"
 #include "xmalloc.h"

 #include <openssl/md5.h>

 /*
  * This is used by SSH1:
  *
  * What kind of triple DES are these 2 routines?
  *
  * Why is there a redundant initialization vector?
  *
  * If only iv3 was used, then, this would till effect have been
  * outer-cbc. However, there is also a private iv1 == iv2 which
  * perhaps makes differential analysis easier. On the other hand, the
  * private iv1 probably makes the CRC-32 attack ineffective. This is a
  * result of that there is no longer any known iv1 to use when
  * 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)
 {
 	des_cblock iv1;

 	memcpy(&iv1, iv2, 8);

 	des_cbc_encrypt(src, dest, len, ks1, &iv1, DES_ENCRYPT);
 	memcpy(&iv1, dest + len - 8, 8);

 	des_cbc_encrypt(dest, dest, len, ks2, 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);
 	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)
 {
 	des_cblock iv1;

 	memcpy(&iv1, iv2, 8);

 	des_cbc_encrypt(src, dest, len, ks3, iv3, DES_DECRYPT);
 	memcpy(iv3, src + len - 8, 8);

 	des_cbc_encrypt(dest, dest, len, ks2, iv2, DES_ENCRYPT);
 	memcpy(iv2, dest + len - 8, 8);

 	des_cbc_encrypt(dest, dest, len, ks1, &iv1, DES_DECRYPT);
 	/* memcpy(&iv1, iv2, 8); */
 	/* Note how iv1 == iv2 on entry and exit. */
 }

 /*
  * SSH1 uses a variation on Blowfish, all bytes must be swapped before
  * and after encryption/decryption. Thus the swap_bytes stuff (yuk).
  */
 static void
 swap_bytes(const unsigned char *src, unsigned char *dst_, int n)
 {
 	/* dst must be properly aligned. */
 	u_int32_t *dst = (u_int32_t *) dst_;
 	union {
 		u_int32_t i;
 		char c[4];
 	} t;

 	/* Process 8 bytes every lap. */
 	for (n = n / 8; n > 0; n--) {
 		t.c[3] = *src++;
 		t.c[2] = *src++;
 		t.c[1] = *src++;
 		t.c[0] = *src++;
 		*dst++ = t.i;

 		t.c[3] = *src++;
 		t.c[2] = *src++;
 		t.c[1] = *src++;
 		t.c[0] = *src++;
 		*dst++ = t.i;
 	}
 }

 /*
  * Names of all encryption algorithms.
  * These must match the numbers defined in cipher.h.
  */
 static char *cipher_names[] =
 {
 	"none",
 	"idea",
 	"des",
 	"3des",
 	"tss",
 	"rc4",
 	"blowfish",
 	"reserved",
 	"blowfish-cbc",
 	"3des-cbc",
 	"arcfour",
 	"cast128-cbc"
 };

 /*
  * Returns a bit mask indicating which ciphers are supported by this
  * implementation.  The bit mask has the corresponding bit set of each
  * supported cipher.
  */

 unsigned int
 cipher_mask1()
 {
 	unsigned int mask = 0;
 	mask |= 1 << SSH_CIPHER_3DES;		/* Mandatory */
 	mask |= 1 << SSH_CIPHER_BLOWFISH;
 	return mask;
 }
 unsigned int
 cipher_mask2()
 {
 	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;
 	return mask;
 }
 unsigned int
 cipher_mask()
 {
 	return cipher_mask1() | cipher_mask2();
 }

 /* Returns the name of the cipher. */

 const char *
 cipher_name(int cipher)
 {
 	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];
 }

 /* Returns 1 if the name of the ciphers are valid. */

 #define	CIPHER_SEP	","
 int
 ciphers_valid(const char *names)
 {
 	char *ciphers;
 	char *p;
 	int i;

 	if (names == NULL || strcmp(names, "") == 0)
 		return 0;
 	ciphers = xstrdup(names);
 	for ((p = strtok(ciphers, CIPHER_SEP)); p; (p = strtok(NULL, CIPHER_SEP))) {
 		i = cipher_number(p);
 		if (i == -1 || !(cipher_mask2() & (1 << i))) {
 			xfree(ciphers);
 			return 0;
 		}
 	}
 	xfree(ciphers);
 	return 1;
 }

 /*
  * Parses the name of the cipher.  Returns the number of the corresponding
  * cipher, or -1 on error.
  */

 int
 cipher_number(const char *name)
 {
 	int i;
 	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;
 }

 /*
  * 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)
 {
 	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));
 }

 /* 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));
 }

 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));
 	}
 }

 /* Encrypts data using the cipher. */

 void
 cipher_encrypt(CipherContext *context, unsigned char *dest,
 	       const unsigned char *src, unsigned 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));
 	}
 }

 /* Decrypts data using the cipher. */

 void
 cipher_decrypt(CipherContext *context, unsigned char *dest,
 	       const unsigned char *src, unsigned int len)
 {
 	if ((len & 7) != 0)
 		fatal("cipher_decrypt: bad ciphertext length %d", len);

 	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));
 	}
 }
	/*
	*
	* cipher.c
	*
	* Author: Tatu Ylonen <ylo@cs.hut.fi>
	*
	* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
	* All rights reserved
	*
	* Created: Wed Apr 19 17:41:39 1995 ylo
	*
	*/

	#include "includes.h"
	RCSID("$OpenBSD: cipher.c,v 1.28 2000/06/20 01:39:40 markus Exp $");

	#include "ssh.h"
	#include "cipher.h"
	#include "xmalloc.h"

	#include <openssl/md5.h>

	/*
	* This is used by SSH1:
	*
	* What kind of triple DES are these 2 routines?
	*
	* Why is there a redundant initialization vector?
	*
	* If only iv3 was used, then, this would till effect have been
	* outer-cbc. However, there is also a private iv1 == iv2 which
	* perhaps makes differential analysis easier. On the other hand, the
	* private iv1 probably makes the CRC-32 attack ineffective. This is a
	* result of that there is no longer any known iv1 to use when
	* 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)
	{
	des_cblock iv1;

	memcpy(&iv1, iv2, 8);

	des_cbc_encrypt(src, dest, len, ks1, &iv1, DES_ENCRYPT);
	memcpy(&iv1, dest + len - 8, 8);

	des_cbc_encrypt(dest, dest, len, ks2, 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);
	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)
	{
	des_cblock iv1;

	memcpy(&iv1, iv2, 8);

	des_cbc_encrypt(src, dest, len, ks3, iv3, DES_DECRYPT);
	memcpy(iv3, src + len - 8, 8);

	des_cbc_encrypt(dest, dest, len, ks2, iv2, DES_ENCRYPT);
	memcpy(iv2, dest + len - 8, 8);

	des_cbc_encrypt(dest, dest, len, ks1, &iv1, DES_DECRYPT);
	/* memcpy(&iv1, iv2, 8); */
	/* Note how iv1 == iv2 on entry and exit. */
	}

	/*
	* SSH1 uses a variation on Blowfish, all bytes must be swapped before
	* and after encryption/decryption. Thus the swap_bytes stuff (yuk).
	*/
	static void
	swap_bytes(const unsigned char src, unsigned char dst_, int n)
	{
	/* dst must be properly aligned. */
	u_int32_t dst = (u_int32_t ) dst_;
	union {
	u_int32_t i;
	char c[4];
	} t;

	/* Process 8 bytes every lap. */
	for (n = n / 8; n > 0; n--) {
	t.c[3] = *src++;
	t.c[2] = *src++;
	t.c[1] = *src++;
	t.c[0] = *src++;
	*dst++ = t.i;

	t.c[3] = *src++;
	t.c[2] = *src++;
	t.c[1] = *src++;
	t.c[0] = *src++;
	*dst++ = t.i;
	}
	}

	/*
	* Names of all encryption algorithms.
	* These must match the numbers defined in cipher.h.
	*/
	static char *cipher_names[] =
	{
	"none",
	"idea",
	"des",
	"3des",
	"tss",
	"rc4",
	"blowfish",
	"reserved",
	"blowfish-cbc",
	"3des-cbc",
	"arcfour",
	"cast128-cbc"
	};

	/*
	* Returns a bit mask indicating which ciphers are supported by this
	* implementation. The bit mask has the corresponding bit set of each
	* supported cipher.
	*/

	unsigned int
	cipher_mask1()
	{
	unsigned int mask = 0;
	mask \|= 1 << SSH_CIPHER_3DES; /* Mandatory */
	mask \|= 1 << SSH_CIPHER_BLOWFISH;
	return mask;
	}
	unsigned int
	cipher_mask2()
	{
	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;
	return mask;
	}
	unsigned int
	cipher_mask()
	{
	return cipher_mask1() \| cipher_mask2();
	}

	/* Returns the name of the cipher. */

	const char *
	cipher_name(int cipher)
	{
	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];
	}

	/* Returns 1 if the name of the ciphers are valid. */

	#define CIPHER_SEP ","
	int
	ciphers_valid(const char *names)
	{
	char *ciphers;
	char *p;
	int i;

	if (names == NULL \|\| strcmp(names, "") == 0)
	return 0;
	ciphers = xstrdup(names);
	for ((p = strtok(ciphers, CIPHER_SEP)); p; (p = strtok(NULL, CIPHER_SEP))) {
	i = cipher_number(p);
	if (i == -1 \|\| !(cipher_mask2() & (1 << i))) {
	xfree(ciphers);
	return 0;
	}
	}
	xfree(ciphers);
	return 1;
	}

	/*
	* Parses the name of the cipher. Returns the number of the corresponding
	* cipher, or -1 on error.
	*/

	int
	cipher_number(const char *name)
	{
	int i;
	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;
	}

	/*
	* 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)
	{
	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));
	}

	/* 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));
	}

	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));
	}
	}

	/* Encrypts data using the cipher. */

	void
	cipher_encrypt(CipherContext context, unsigned char dest,
	const unsigned char *src, unsigned 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));
	}
	}

	/* Decrypts data using the cipher. */

	void
	cipher_decrypt(CipherContext context, unsigned char dest,
	const unsigned char *src, unsigned int len)
	{
	if ((len & 7) != 0)
	fatal("cipher_decrypt: bad ciphertext length %d", len);

	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));
	}
	}