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#!/bin/bash
# base64.sh: Bash implementation of Base64 encoding and decoding.
#
# Copyright (c) 2011 vladz <vladz@devzero.fr>
# Used in ABSG with permission (thanks!).
#
# Encode or decode original Base64 (and also Base64url)
#+ from STDIN to STDOUT.
#
# Usage:
#
# Encode
# $ ./base64.sh < binary-file > binary-file.base64
# Decode
# $ ./base64.sh -d < binary-file.base64 > binary-file
#
# Reference:
#
# [1] RFC4648 - "The Base16, Base32, and Base64 Data Encodings"
# http://tools.ietf.org/html/rfc4648#section-5
# The base64_charset[] array contains entire base64 charset,
# and additionally the character "=" ...
base64_charset=( {A..Z} {a..z} {0..9} + / = )
# Nice illustration of brace expansion.
# Uncomment the ### line below to use base64url encoding instead of
#+ original base64.
### base64_charset=( {A..Z} {a..z} {0..9} - _ = )
# Output text width when encoding
#+ (64 characters, just like openssl output).
text_width=64
function display_base64_char {
# Convert a 6-bit number (between 0 and 63) into its corresponding values
#+ in Base64, then display the result with the specified text width.
printf "${base64_charset[$1]}"; (( width++ ))
(( width % text_width == 0 )) && printf "\n"
}
function encode_base64 {
# Encode three 8-bit hexadecimal codes into four 6-bit numbers.
# We need two local int array variables:
# c8[]: to store the codes of the 8-bit characters to encode
# c6[]: to store the corresponding encoded values on 6-bit
declare -a -i c8 c6
# Convert hexadecimal to decimal.
c8=( $(printf "ibase=16; ${1:0:2}\n${1:2:2}\n${1:4:2}\n" | bc) )
# Let's play with bitwise operators
#+ (3x8-bit into 4x6-bits conversion).
(( c6[0] = c8[0] >> 2 ))
(( c6[1] = ((c8[0] & 3) << 4) | (c8[1] >> 4) ))
# The following operations depend on the c8 element number.
case ${#c8[*]} in
3) (( c6[2] = ((c8[1] & 15) << 2) | (c8[2] >> 6) ))
(( c6[3] = c8[2] & 63 )) ;;
2) (( c6[2] = (c8[1] & 15) << 2 ))
(( c6[3] = 64 )) ;;
1) (( c6[2] = c6[3] = 64 )) ;;
esac
for char in ${c6[@]}; do
display_base64_char ${char}
done
}
function decode_base64 {
# Decode four base64 characters into three hexadecimal ASCII characters.
# c8[]: to store the codes of the 8-bit characters
# c6[]: to store the corresponding Base64 values on 6-bit
declare -a -i c8 c6
# Find decimal value corresponding to the current base64 character.
for current_char in ${1:0:1} ${1:1:1} ${1:2:1} ${1:3:1}; do
[ "${current_char}" = "=" ] && break
position=0
while [ "${current_char}" != "${base64_charset[${position}]}" ]; do
(( position++ ))
done
c6=( ${c6[*]} ${position} )
done
# Let's play with bitwise operators
#+ (4x8-bit into 3x6-bits conversion).
(( c8[0] = (c6[0] << 2) | (c6[1] >> 4) ))
# The next operations depends on the c6 elements number.
case ${#c6[*]} in
3) (( c8[1] = ( (c6[1] & 15) << 4) | (c6[2] >> 2) ))
(( c8[2] = (c6[2] & 3) << 6 )); unset c8[2] ;;
4) (( c8[1] = ( (c6[1] & 15) << 4) | (c6[2] >> 2) ))
(( c8[2] = ( (c6[2] & 3) << 6) | c6[3] )) ;;
esac
for char in ${c8[*]}; do
printf "\x$(printf "%x" ${char})"
done
}
# main ()
if [ "$1" = "-d" ]; then # decode
# Reformat STDIN in pseudo 4x6-bit groups.
content=$(cat - | tr -d "\n" | sed -r "s/(.{4})/\1 /g")
for chars in ${content}; do decode_base64 ${chars}; done
else
# Make a hexdump of stdin and reformat in 3-byte groups.
content=$(cat - | xxd -ps -u | sed -r "s/(\w{6})/\1 /g" |
tr -d "\n")
for chars in ${content}; do encode_base64 ${chars}; done
echo
fi
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