#include "sha1.h"

#ifdef __KERNEL__
#define __NO_VERSION__
#endif /* __KERNEL__ */

#define DevccBlockSize 32

/* internal utility functions */

static int copy_16(uint8_t *buf, uint16_t data, int offset) {
  buf[offset] = (data >> 8) & 0xff;
  buf[offset+1] = data & 0xff;
  return offset+2;
}

static int copy_32(uint8_t *buf, uint32_t data, int offset) {
  buf[offset] = (data >> 24) & 0xff;
  buf[offset+1] = (data >> 16) & 0xff;
  buf[offset+2] = (data >> 8) & 0xff;
  buf[offset+3] = data & 0xff;
  return offset+4;
}

/*
 * SHA1
 *
 * Description:
 *     This fuction will return the SHA1 hash of a message.
 *
 * Parameters:
 *     digest: [out]
 *         Where the digest is returned.
 *     message: [in]
 *         The message to be hashed.
 *     message_length: [in]
 *         The length of the message (in bytes).
 *
 *  Returns:
 *      0 on success.
 *     -1 on error.  (I don't think this ever happens) 
 */     

int SHA1( uint8_t digest[SHA1HashSize], 
	  const uint8_t *message, 
	  int message_length) 
{

  SHA1Context ctx;
  int err;

  err = SHA1Reset(&ctx);
  if (err) 
    return -1;

  err = SHA1Input(&ctx, message, message_length);
  if (err) 
    return -1;

  err = SHA1Result(&ctx,digest);
  if (err) 
    return -1;
 
  return 0;
}

/*
 *  devcc_validate_checksum
 *
 *  Description:
 *      This function will compute a checksum by taking the first 4 bytes of 
 *      the SHA1 hash of the first 28 bytes of a message.  It will then 
 *      return 1 if this checksum matches the 29th-32nd bytes of the message.
 *
 *  Parameters:
 *      message: [in]
 *          The message to be validated.
 *
 *  Returns:
 *      1 if the checksum matches bytes 29-32.
 *      0 otherwise.
 */

int devcc_validate_checksum(uint8_t *buffer) {
  uint8_t md[SHA1HashSize];

  (void) SHA1(md,buffer,DevccBlockSize-4);

  if (md[0] == buffer[DevccBlockSize-4] &&
      md[1] == buffer[DevccBlockSize-3] &&
      md[2] == buffer[DevccBlockSize-2] &&
      md[3] == buffer[DevccBlockSize-1])
    return 1;
  else
    return 0;
}

/*
 *  devcc_append_checksum
 *
 *  Description:
 *      This function will compute a checksum by taking the first 4 bytes of 
 *      the SHA1 hash of the first 28 bytes of a message.  It will then 
 *      write this checksum into the 29th-32nd bytes of the message, thus
 *      producing a message that will produce true when passed to
 *      devcc_validate_checksum.
 *
 *  Parameters:
 *      message: [in/out]
 *          The message to be checksumed.
 *
 *  Returns:
 *      Nothing.
 */

void devcc_append_checksum(uint8_t *buffer) {
  uint8_t md[SHA1HashSize];

  (void) SHA1(md,buffer,DevccBlockSize-4);

  buffer[DevccBlockSize-4] = md[0];
  buffer[DevccBlockSize-3] = md[1];
  buffer[DevccBlockSize-2] = md[2];
  buffer[DevccBlockSize-1] = md[3];
}

/*
 *  get_index
 *
 *  Description:
 *      This fuction will return the index of the bit in the current
 *      message block in terms of the packet headers.
 *
 *  Parameters:
 *      scrport: [in]
 *          TCP source port as specified in the packet header.
 *      dstport: [in]
 *          TCP destination port as specified in the packet header.
 *      seq: [in]
 *          TCP sequence number as specified in the packet header.
 *      key: [in]
 *         Byte array to be used as the secret key.
 *      keylen: [in]
 *          Length of the key (in bytes).
 *
 *  Returns:
 *      The index of the bit associated with these packet headers.
 */     

int get_index (uint16_t srcport, 
	       uint16_t dstport, 
	       uint32_t seq, 
	       uint8_t *key, int keylen) {
  
  uint8_t buf[8+keylen];
  uint8_t md[SHA1HashSize];
  int i, off;
  
  off = 0;
  off = copy_16(buf,srcport,off);
  off = copy_16(buf,dstport,off);
  off = copy_32(buf,seq,off);
  
  for(i=0;i<keylen;i++) {
    buf[off]=key[i];
    off++;
  }

  (void) SHA1(md,buf,off);
    
  /*FIXME: This assumes a 32 byte DevccBlockSize */
  return md[0];
}

/*
 *  get_key_bit
 *
 *  Description:
 *      This fuction will return the key bit for this packet in terms 
 *      of the packet headers.
 *
 *  Parameters:
 *      scrport: [in]
 *          TCP source port as specified in the packet header.
 *      dstport: [in]
 *          TCP destination port as specified in the packet header.
 *      seq: [in]
 *          TCP sequence number as specified in the packet header.
 *      ack: [in]
 *          TCP acknowledgement number as specified in the packet header.
 *      window: [in]
 *          TCP window as specified in the packet header.
 *      chksum: [in]
 *          TCP check sum as specified in the packet header.
 *      ts: [in]
 *          TCP timestamp as specified in the packet header.
 *      tsreply: [in]
 *          TCP timestamp echo reply as specified in the packet header.
 *      key: [in]
 *         Byte array to be used as the secret key.
 *      keylen: [in]
 *          Length of the key (in bytes).
 *
 *  Returns:
 *      The key bit associated with these packet headers.
 */     

int get_key_bit  (uint16_t srcport, 
                  uint16_t dstport, 
                  uint32_t seq, 
                  uint32_t ack, 
                  uint16_t window, 
                  uint16_t chksum,
                  uint32_t ts,
                  uint32_t tsreply, 
                  uint8_t *key, int keylen) {
  
  uint8_t buf[24+keylen];
  uint8_t md[SHA1HashSize];
  int i, off;

  off = 0;
  off = copy_16(buf,srcport,off);
  off = copy_16(buf,dstport,off);
  off = copy_32(buf,seq,off);
  off = copy_32(buf,ack,off);
  off = copy_16(buf,window,off);
  off = copy_16(buf,chksum,off);
  off = copy_32(buf,ts,off);
  off = copy_32(buf,tsreply,off);  

  for(i=0;i<keylen;i++) {
    buf[off]=key[i];
    off++;
  }

  (void) SHA1(md,buf,off);
    
  return (md[0] >> 7) & 0x01;
}