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1 files changed, 304 insertions, 0 deletions

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+/*
+
+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("$Id: cipher.c,v 1.1 1999/10/27 03:42:44 damien Exp $");
+
+#include "ssh.h"
+#include "cipher.h"
+
+#include <openssl/md5.h>
+
+/*
+ * What kind of tripple 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, 
+                 void *dest, void *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,
+                 void *dest, void *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. */
+}
+
+/*
+ * SSH 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)
+{
+  u_int32_t *dst = (u_int32_t *)dst_;   /* dst must be properly aligned. */
+  union {
+    u_int32_t i;
+    char c[4];
+  } t;
+
+  /* assert((n & 7) == 0); */
+
+  /* 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;
+    }
+}
+
+void (*cipher_attack_detected)(const char *fmt, ...) = fatal;
+
+static inline
+void
+detect_cbc_attack(const unsigned char *src,
+                  unsigned int len)
+{
+  return;
+  
+  log("CRC-32 CBC insertion attack detected");
+  cipher_attack_detected("CRC-32 CBC insertion attack detected");
+}
+
+/* Names of all encryption algorithms.  These must match the numbers defined
+   int cipher.h. */
+static char *cipher_names[] =
+{
+  "none",
+  "idea",
+  "des",
+  "3des",
+  "tss",
+  "rc4",
+  "blowfish"
+};
+
+/* 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_mask()
+{
+  unsigned int mask = 0;
+  mask |= 1 << SSH_CIPHER_3DES; /* Mandatory */
+  mask |= 1 << SSH_CIPHER_BLOWFISH;
+  return mask;
+}
+
+/* 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 number: %d", cipher);
+  return cipher_names[cipher];
+}
+
+/* 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;
+  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, int for_encryption)
+{
+  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, for_encryption);
+  
+  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, int for_encryption)
+{
+  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:
+      BF_set_key(&context->u.bf.key, keylen, padded);
+      memset(context->u.bf.iv, 0, 8);
+      break;
+
+    default:
+      fatal("cipher_set_key: unknown cipher: %d", cipher);
+    }
+  memset(padded, 0, sizeof(padded));
+}
+
+/* Encrypts data using the cipher. */
+
+void cipher_encrypt(CipherContext *context, unsigned char *dest,
+                    const unsigned char *src, unsigned int len)
+{
+  assert((len & 7) == 0);
+
+  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, (void*)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;
+
+    default:
+      fatal("cipher_encrypt: unknown cipher: %d", context->type);
+    }
+}
+  
+/* Decrypts data using the cipher. */
+
+void cipher_decrypt(CipherContext *context, unsigned char *dest,
+                    const unsigned char *src, unsigned int len)
+{
+  assert((len & 7) == 0);
+
+  switch (context->type)
+    {
+    case SSH_CIPHER_NONE:
+      memcpy(dest, src, len);
+      break;
+
+    case SSH_CIPHER_3DES:
+      /* CRC-32 attack? */
+      SSH_3CBC_DECRYPT(context->u.des3.key1,
+                       context->u.des3.key2, &context->u.des3.iv2,
+                       context->u.des3.key3, &context->u.des3.iv3,
+                       dest, (void*)src, len);
+      break;
+
+    case SSH_CIPHER_BLOWFISH:
+      detect_cbc_attack(src, len);
+      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;
+
+    default:
+      fatal("cipher_decrypt: unknown cipher: %d", context->type);
+    }
+}