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Raw Data Conversion
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About Perl pack/unpack

Perl pack/unpack is for pack/unpack to/from raw binary.
As such  pack 'H*' will pack a Hexadecimal String.
while unpack 'H*' will convert a binary into a hexadecmal string
similarly pack 'N' converts a number, 4 byte / 16 bit network number.

  Decimal to Hexidecimal
    perl -le 'print unpack("H*", pack("N", 3735928559))'  # 16 bit number

  Hexadecimal to Decimal
    perl -le 'print unpack("N", pack("H8",substr("0"x8 . "DEADBEEF",-8)));'

  Decimal to
    perl -le 'print unpack("B*", pack("N", 3735928559))'   # 32bit
    perl -le 'printf("%b\n", 223)'                 # variable length
    perl -le 'printf("%08b\n", 123)'               # fixed length

  Binary to Decimal
    perl -le 'print ord(pack('B8', '10110110'))'   # single character only
    perl -le '$b="10111"; print oct( "0b$b" )'     # up to 32bit
                                                # can do larger (with warning)

  Raw binary string to Hexadecimal string  (more in hexidecmial below)
    perl -0777 -e 'print unpack("H*",<>), "\n"'


Other methods...

  Decimal to Hexadeciment (using printf)
    printf '0x%08X\n'  3735928559
    perl -le 'printf("0x%08X\n", 3735928559)'

  Hexadecimal to Decimal
    perl -le 'print hex("DEADBEEF")'

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About using DC

You must specify input base after output base otherwise you will
need to specify the output base number using the input base!

  Hexadecimal to Binary (not raw)
    hex=81
    echo "2o 16i ${hex} p" | dc
    10000001

  Binary to Hexadecimal
    binary=00111100
    echo "16o 2i ${binary} p" | dc
    3C

See..  http://wiki.bash-hackers.org/howto/calculate-dc
Also   http://en.wikipedia.org/wiki/Dc_%28Unix%29

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Hexadecimal

  raw binary to Hexadecimal (For viewing)
    hexdump -

  Hexadecimal to Raw binary (with cleanup)
    perl -pe 'y/A-Fa-f0-9//dc; $_= pack("H*",$_);'

  Raw binary string to Hexadecimal Lines of 64 hexchars
    perl -0777 -pe '$_=unpack("H*",$_); s/.{64}/$&\n/g; s/\n?$/\n/;'


  In C From hex
    void hex_to_binary(unsigned char *buf, unsigned char *hex)
    {
      for( ; sscanf( hex, "%2x", buf++ ) == 1 ; hex+=2 );
      *buf = 0;  // null terminate -- precaution
    }

  In C To Hex
    void print_hex(unsigned char *buf, int len)
    {
      int i;
      int n;

      for(i=0,n=0;i<len;i++){
        //if(n > 7){
        //  printf("\n");
        //  n = 0;
        //}
        printf("%02x",buf[i]);
        //n++;
      }
      printf("\n");
    }


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ModHex  (used by Yubikey's)

Modified (substitute) Hexadecimal

Reason... Keyboards do not know its keymaps! It only sends scancodes
However all keyboards map certain keys to certain scancodes and these are
what yubikeys use.

Basically as it  can only transmit certain keys so a modified hexadecimal is
used to send the Yubikey output.

Hexadecimal:  0123 4567 89ab cdef
ModHex Code:  cbde fghi jkln rtuv

Further 'c' is most ambigious in keyboards,
so any other key should map to '0' when reading a yubikey

As such
  bde fghi jkln rtuv -maps-> 0x1 - 0xf
And all other characters (including 'c') maps to 0x0

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Base64

raw binary to base64 (broken into lines)

   openssl enc -base64

base64 to rawbinary

   openssl enc -base64 -d

Perl Encode
  perl -MMIME::Base64 -e 'print encode_base64("string")'

Perl Decode
  perl -MMIME::Base64 -0777 -ne 'print encode_base64($_)' file


Note that uuencode is almost a substitution coding of Base64
as such the perl pack for uuencode can be used for conversion.
See "Programming Perl"  page 237 (unpack function).
Or my own implementation in "b64decode" and "b64encode" scripts.
The above is easier to handle.

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