Base64 Decoding

Decodes data encoded with MIME base64.

• C#
• VB.Net
• C
• C++
• PHP

									Public Shared Function Base64Decoding(data As Char()) As Byte()
	Dim length As Integer, length2 As Integer, length3 As Integer
	Dim blockCount As Integer
	Dim paddingCount As Integer = 0

	length = data.Length
	blockCount = length \ 4
	length2 = blockCount * 3

	For x As Integer = 0 To 1
		If data(length - x - 1) = "="c Then
			paddingCount += 1
		End If
	Next

	Dim buffer As Byte() = New Byte(length - 1) {}
	Dim buffer2 As Byte() = New Byte(length2 - 1) {}

	For x As Integer = 0 To length - 1
		buffer(x) = CharToSixBit(data(x))
	Next

	Dim b As Byte, b1 As Byte, b2 As Byte, b3 As Byte
	Dim temp1 As Byte, temp2 As Byte, temp3 As Byte, temp4 As Byte

	For x As Integer = 0 To blockCount - 1
		temp1 = buffer(x * 4)
		temp2 = buffer(x * 4 + 1)
		temp3 = buffer(x * 4 + 2)
		temp4 = buffer(x * 4 + 3)

		b = CByte(temp1 << 2)
		b1 = CByte((temp2 And 48) >> 4)
		b1 += b

		b = CByte((temp2 And 15) << 4)
		b2 = CByte((temp3 And 60) >> 2)
		b2 += b

		b = CByte((temp3 And 3) << 6)
		b3 = temp4
		b3 += b

		buffer2(x * 3) = b1
		buffer2(x * 3 + 1) = b2
		buffer2(x * 3 + 2) = b3
	Next

	length3 = length2 - paddingCount
	Dim result As Byte() = New Byte(length3 - 1) {}

	For x As Integer = 0 To length3 - 1
		result(x) = buffer2(x)
	Next

	Return result
End Function

Private Shared Function CharToSixBit(c As Char) As Byte
	Dim lookupTable As Char() = New Char(63) {"A"c, "B"c, "C"c, "D"c, "E"c, "F"c, _
		"G"c, "H"c, "I"c, "J"c, "K"c, "L"c, _
		"M"c, "N"c, "O"c, "P"c, "Q"c, "R"c, _
		"S"c, "T"c, "U"c, "V"c, "W"c, "X"c, _
		"Y"c, "Z"c, "a"c, "b"c, "c"c, "d"c, _
		"e"c, "f"c, "g"c, "h"c, "i"c, "j"c, _
		"k"c, "l"c, "m"c, "n"c, "o"c, "p"c, _
		"q"c, "r"c, "s"c, "t"c, "u"c, "v"c, _
		"w"c, "x"c, "y"c, "z"c, "0"c, "1"c, _
		"2"c, "3"c, "4"c, "5"c, "6"c, "7"c, _
		"8"c, "9"c, "+"c, "/"c}

	If c = "="c Then
		Return 0
	Else
		For x As Integer = 0 To 63
			If lookupTable(x) = c Then
				Return CByte(x)
			End If
		Next

		Return 0
	End If
End Function
								

Example

									Dim data = "amRmZ3NkaGZzZGZzZCA2NDQ1ZHNmc2Q3ZmcvKi8rYmZqc2RnZiUkXg=="
Dim value = Base64Decoding(data.ToCharArray())
								

Output

									jdfgsdhfsdfsd 6445dsfsd7fg/*/+bfjsdgf%$^