Base64S

# Algorithm

Encrypting

1. Calculate the difference in length of byte array len(key) - len(src). If the result is a negative value, it is treated as 0.
2. XOR the source and key byte arrays in order and stores into a newly-allocated byte array.
3. Stores the result of (1) in the last byte.
4. Encode the byte array of (3) into a newly-allocated byte array using the Base64 encoding scheme.

Decrypting

Manipulate in the opposite way.

# Examples

Normal Base64

Source Text (UTF-8) a b c
Source octets 97 (0x61) 98 (0x62) 99 (0x63)
Bit pattern 0 1 1 0 0 0 0 1 0 1 1 0 0 0 1 0 0 1 1 0 0 0 1 1
Index 24 22 9 35
Base64-encoded Y W J j
Encoded octets 89 (0x59)
01011001		 87 (0x57)
01010111		 74 (0x4A)
01001010		 106 (0x6A)
01101010

Base64S : src = abc / key = xyz (src.length = key.length)

Source Text (UTF-8) a b c
Octets 97 (0x61) 98 (0x62) 99 (0x63)
Bit pattern 0 1 1 0 0 0 0 1 0 1 1 0 0 0 1 0 0 1 1 0 0 0 1 1
Key Text (UTF-8) x y z
Octets 120 (0x78)121 (0x79)122 (0x7A)
Bit pattern 0 1 1 1 1 0 0 0 0 1 1 1 1 0 1 1 0 1 1 1 1 0 1 0
Bitwise op.   97 XOR 120 = 25 97 XOR 121 = 24 99 XOR 122 = 25 key.len - src.len
Bit pattern 0 0 0 1 1 0 0 1 0 0 0 1 1 0 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0                        
Output Index 6 17 44 25 0 0 Padding Padding
Base64-encoded G R s Z A A = =
Encoded octets 71 (0x47)
01000111		 82 (0x52)
01010010		 115 (0x73)
01110011S		 90 (0x5A)
01011010		 65 (0x41)
01000001		 65 (0x41)
01000001		 61 (0x3D)
00111101		 61 (0x3D)
00111101

Base64S : src = abcde / key = xyz (src.length > key.length)

Source Text (UTF-8) a b c d e
Octets 97 (0x61) 98 (0x62) 99 (0x63) 100 (0x64) 101 (0x65)
Bit pattern 0 1 1 0 0 0 0 1 0 1 1 0 0 0 1 0 0 1 1 0 0 0 1 1 0 1 1 0 0 1 0 0 0 1 1 0 0 1 0 1
Key Text (UTF-8) x y z x y
Octets 120 (0x78) 121 (0x79) 122 (0x7A) 120 (0x78) 121 (0x79)
Bit pattern 0 1 1 1 1 0 0 0 0 1 1 1 1 0 1 1 0 1 1 1 1 0 1 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 1 1
Bitwise op.   97 XOR 120 = 25 97 XOR 121 = 24 99 XOR 122 = 25 100 XOR 120 = 28 101 XOR 121 = 28 key.len - src.len
Bit pattern 0 0 0 1 1 0 0 0 0 0 0 1 1 0 1 1 0 0 0 1 1 0 0 1 0 0 0 1 1 1 0 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0
Output Index 6 17 44 25 7 1 48 0
Base64-encoded G R s Z H B w A
Encoded octets 71 (0x47)
01000111		 82 (0x52)
01010010		 115 (0x73)
01110011		 90 (0x5A)
01011010		 72 (0x48)
01001000		 66 (0x42)
01000010		 119 (0x77)
01110111		 65 (0x41)
01000001

Base64S : src = ab / key = xyz (src.length < key.length)

Source Text (UTF-8) a b Padding bits
Octets 97 (0x61) 98 (0x62)
Bit pattern 0 1 1 0 0 0 0 1 0 1 1 0 0 0 1 0 1 1 1 1 1 1 1 1
Key Text (UTF-8) x y z
Octets 120 (0x78)121 (0x79)122 (0x7A)
Bit pattern 0 1 1 1 1 0 0 0 0 1 1 1 1 0 1 1 0 1 1 1 1 0 1 0
Bitwise op.   97 XOR 120 = 25 97 XOR 121 = 24 255 XOR 122 = 133 len(key) - len(src)
Bit pattern 0 0 0 1 1 0 0 1 0 0 0 1 1 0 0 0 1 0 0 0 0 1 0 1 0 0 0 0 0 0 0 1 0 0 0 0                        
Output Index 6 17 46 5 0 16 Padding Padding
Base64-encoded G R u F A Q = =
Encoded octets 71 (0x47)
01000111		 82 (0x52)
01010010		 117 (0x75)
01000110		 70 (0x46)
01000110		 65 (0x41)
01000001		 81 (0x51)
01010001		 61 (0x3D)
00111101		 61 (0x3D)
00111101

# Implementation

Java, JavaScript, Python, PowerShell, VBA implementations are available on GitHub.

Apache Maven

JAR direct download
base64s-1.1.1.jar (4,050 bytes / Compiled with JDK8)
SHA-1: 335e423f284cda1ba95cdb9a860c28776708e001
SHA-256: 306cdf48b74afa30462eecd6abc84f6b0c6625a6aa1fa8cbc0d224f24dc4cd6d

# Notice

Base64S is not intended to be used where secrecy is of any concern.

x
The Base 64 Alphabet

IDX BIN     ENC   IDX BIN     ENC   IDX BIN     ENC   IDX BIN     ENC
 0  000000  A     16  010000  Q     32  100000  g     48  110000  w
 1  000001  B     17  010001  R     33  100001  h     49  110001  x
 2  000010  C     18  010010  S     34  100010  i     50  110010  y
 3  000011  D     19  010011  T     35  100011  j     51  110011  z
 4  000100  E     20  010100  U     36  100100  k     52  110100  0
 5  000101  F     21  010101  V     37  100101  l     53  110101  1
 6  000110  G     22  010110  W     38  100110  m     54  110110  2
 7  000111  H     23  010111  X     39  100111  n     55  110111  3
 8  001000  I     24  011000  Y     40  101000  o     56  111000  4
 9  001001  J     25  011001  Z     41  101001  p     57  111001  5
10  001010  K     26  011010  a     42  101010  q     58  111010  6
11  001011  L     27  011011  b     43  101011  r     59  111011  7
12  001100  M     28  011100  c     44  101100  s     60  111100  8
13  001101  N     29  011101  d     45  101101  t     61  111101  9
14  001110  O     30  011110  e     46  101110  u     62  111110  +
15  001111  P     31  011111  f     47  101111  v     63  111111  /
                                                      (pad)       =