Base32 Decoding
https://stackoverflow.com/questions/641361
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I have a base32 string which I need to convert to a byte array. And I'm having trouble finding a conversion method in the .NET framework. I can find methods for base64 but not for base32.
Convert.FromBase64String – something like this for base32 would be perfect.
Is there such a method in the framework or do I have to roll my own?
Solution
Check this FromBase32String implementation for .NET found here.
Edit: The above link was dead; you can find an archived copy at archive.org
The actual code read:
using System;
using System.Text;
public sealed class Base32 {
// the valid chars for the encoding
private static string ValidChars = "QAZ2WSX3" + "EDC4RFV5" + "TGB6YHN7" + "UJM8K9LP";
/// <summary>
/// Converts an array of bytes to a Base32-k string.
/// </summary>
public static string ToBase32String(byte[] bytes) {
StringBuilder sb = new StringBuilder(); // holds the base32 chars
byte index;
int hi = 5;
int currentByte = 0;
while (currentByte < bytes.Length) {
// do we need to use the next byte?
if (hi > 8) {
// get the last piece from the current byte, shift it to the right
// and increment the byte counter
index = (byte)(bytes[currentByte++] >> (hi - 5));
if (currentByte != bytes.Length) {
// if we are not at the end, get the first piece from
// the next byte, clear it and shift it to the left
index = (byte)(((byte)(bytes[currentByte] << (16 - hi)) >> 3) | index);
}
hi -= 3;
} else if(hi == 8) {
index = (byte)(bytes[currentByte++] >> 3);
hi -= 3;
} else {
// simply get the stuff from the current byte
index = (byte)((byte)(bytes[currentByte] << (8 - hi)) >> 3);
hi += 5;
}
sb.Append(ValidChars[index]);
}
return sb.ToString();
}
/// <summary>
/// Converts a Base32-k string into an array of bytes.
/// </summary>
/// <exception cref="System.ArgumentException">
/// Input string <paramref name="s">s</paramref> contains invalid Base32-k characters.
/// </exception>
public static byte[] FromBase32String(string str) {
int numBytes = str.Length * 5 / 8;
byte[] bytes = new Byte[numBytes];
// all UPPERCASE chars
str = str.ToUpper();
int bit_buffer;
int currentCharIndex;
int bits_in_buffer;
if (str.Length < 3) {
bytes[0] = (byte)(ValidChars.IndexOf(str[0]) | ValidChars.IndexOf(str[1]) << 5);
return bytes;
}
bit_buffer = (ValidChars.IndexOf(str[0]) | ValidChars.IndexOf(str[1]) << 5);
bits_in_buffer = 10;
currentCharIndex = 2;
for (int i = 0; i < bytes.Length; i++) {
bytes[i] = (byte)bit_buffer;
bit_buffer >>= 8;
bits_in_buffer -= 8;
while (bits_in_buffer < 8 && currentCharIndex < str.Length) {
bit_buffer |= ValidChars.IndexOf(str[currentCharIndex++]) << bits_in_buffer;
bits_in_buffer += 5;
}
}
return bytes;
}
}
OTHER TIPS
I had a need for a base32 encoder/decoder, so I spent a couple hours this afternoon throwing this together. I believe it conforms to the standards listed here: http://tools.ietf.org/html/rfc4648#section-6.
public class Base32Encoding
{
public static byte[] ToBytes(string input)
{
if (string.IsNullOrEmpty(input))
{
throw new ArgumentNullException("input");
}
input = input.TrimEnd('='); //remove padding characters
int byteCount = input.Length * 5 / 8; //this must be TRUNCATED
byte[] returnArray = new byte[byteCount];
byte curByte = 0, bitsRemaining = 8;
int mask = 0, arrayIndex = 0;
foreach (char c in input)
{
int cValue = CharToValue(c);
if (bitsRemaining > 5)
{
mask = cValue << (bitsRemaining - 5);
curByte = (byte)(curByte | mask);
bitsRemaining -= 5;
}
else
{
mask = cValue >> (5 - bitsRemaining);
curByte = (byte)(curByte | mask);
returnArray[arrayIndex++] = curByte;
curByte = (byte)(cValue << (3 + bitsRemaining));
bitsRemaining += 3;
}
}
//if we didn't end with a full byte
if (arrayIndex != byteCount)
{
returnArray[arrayIndex] = curByte;
}
return returnArray;
}
public static string ToString(byte[] input)
{
if (input == null || input.Length == 0)
{
throw new ArgumentNullException("input");
}
int charCount = (int)Math.Ceiling(input.Length / 5d) * 8;
char[] returnArray = new char[charCount];
byte nextChar = 0, bitsRemaining = 5;
int arrayIndex = 0;
foreach (byte b in input)
{
nextChar = (byte)(nextChar | (b >> (8 - bitsRemaining)));
returnArray[arrayIndex++] = ValueToChar(nextChar);
if (bitsRemaining < 4)
{
nextChar = (byte)((b >> (3 - bitsRemaining)) & 31);
returnArray[arrayIndex++] = ValueToChar(nextChar);
bitsRemaining += 5;
}
bitsRemaining -= 3;
nextChar = (byte)((b << bitsRemaining) & 31);
}
//if we didn't end with a full char
if (arrayIndex != charCount)
{
returnArray[arrayIndex++] = ValueToChar(nextChar);
while (arrayIndex != charCount) returnArray[arrayIndex++] = '='; //padding
}
return new string(returnArray);
}
private static int CharToValue(char c)
{
int value = (int)c;
//65-90 == uppercase letters
if (value < 91 && value > 64)
{
return value - 65;
}
//50-55 == numbers 2-7
if (value < 56 && value > 49)
{
return value - 24;
}
//97-122 == lowercase letters
if (value < 123 && value > 96)
{
return value - 97;
}
throw new ArgumentException("Character is not a Base32 character.", "c");
}
private static char ValueToChar(byte b)
{
if (b < 26)
{
return (char)(b + 65);
}
if (b < 32)
{
return (char)(b + 24);
}
throw new ArgumentException("Byte is not a value Base32 value.", "b");
}
}
I've written some flexible standards based implementations of various Base32 and Base64 encoding/decoding methods. Notably: base64url (per rfc4648) and its base32 equivalent.
By default the Base32Url class encodes with only the characters A to Z and 2 to 7. No hyphens, underscores, pluses, slashes or equals are used, making it usable as a URL token in almost all circumstances. Base32Url also supports custom alphabets, case sensitivity/insensitivity, padding/no-padding etc.
This is a really old question, but I happened to stumble on it wanting the same thing for OTP tokens. It turns out that there is base 32 functionality built into the OTP.NET package on NuGet:
Base32Encoding.ToBytes("(your base 32 string here)")
The reverse is also possible:
Base32Encoding.ToString(new byte[] { /* your bytes here */ })
Here's my quickly jotted solution. It only works on strings that are a multiple of 8 base32 characters. Does work, though.
public class Base32
{
/// <summary>
/// Decode a Base32 string
/// This will only work on a multiple of 40 bits (5 bytes)
/// http://www.garykessler.net/library/base64.html
/// </summary>
public static byte[] Decode(string Base32String)
{
// Ignore hyphens
string str = Base32String.Replace("-", "");
// Convert it to bits
List<byte> bits = new List<byte>();
foreach (char c in str)
{
int i = CharToValue(c);
bits.Add((byte)((i & 16) > 0 ? 1 : 0));
bits.Add((byte)((i & 8) > 0 ? 1 : 0));
bits.Add((byte)((i & 4) > 0 ? 1 : 0));
bits.Add((byte)((i & 2) > 0 ? 1 : 0));
bits.Add((byte)((i & 1) > 0 ? 1 : 0));
}
// Convert bits into bytes
List<byte> bytes = new List<byte>();
for (int i = 0; i < bits.Count; i += 8)
{
bytes.Add((byte)(
(bits[i + 0] << 7) +
(bits[i + 1] << 6) +
(bits[i + 2] << 5) +
(bits[i + 3] << 4) +
(bits[i + 4] << 3) +
(bits[i + 5] << 2) +
(bits[i + 6] << 1) +
(bits[i + 7] << 0)));
}
return bytes.ToArray();
}
static int CharToValue(char c)
{
char cl = char.ToLower(c);
if (cl == 'a') return 0;
if (cl == 'b') return 1;
if (cl == 'c') return 2;
if (cl == 'd') return 3;
if (cl == 'e') return 4;
if (cl == 'f') return 5;
if (cl == 'g') return 6;
if (cl == 'h') return 7;
if (cl == 'i') return 8;
if (cl == 'j') return 9;
if (cl == 'k') return 10;
if (cl == 'l') return 11;
if (cl == 'm') return 12;
if (cl == 'n') return 13;
if (cl == 'o') return 14;
if (cl == 'p') return 15;
if (cl == 'q') return 16;
if (cl == 'r') return 17;
if (cl == 's') return 18;
if (cl == 't') return 19;
if (cl == 'u') return 20;
if (cl == 'v') return 21;
if (cl == 'w') return 22;
if (cl == 'x') return 23;
if (cl == 'y') return 24;
if (cl == 'z') return 25;
if (cl == '2') return 26;
if (cl == '3') return 27;
if (cl == '4') return 28;
if (cl == '5') return 29;
if (cl == '6') return 30;
if (cl == '7') return 31;
throw new Exception("Not a base32 string");
}
}
Here are my functions for encoding and decoding. I feel that they are much shorter and concise than the other suggestions. So if you need a small one, try these.
public static string BytesToBase32(byte[] bytes) {
const string alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
string output = "";
for (int bitIndex = 0; bitIndex < bytes.Length * 8; bitIndex += 5) {
int dualbyte = bytes[bitIndex / 8] << 8;
if (bitIndex / 8 + 1 < bytes.Length)
dualbyte |= bytes[bitIndex / 8 + 1];
dualbyte = 0x1f & (dualbyte >> (16 - bitIndex % 8 - 5));
output += alphabet[dualbyte];
}
return output;
}
public static byte[] Base32ToBytes(string base32) {
const string alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
List<byte> output = new List<byte>();
char[] bytes = base32.ToCharArray();
for (int bitIndex = 0; bitIndex < base32.Length * 5; bitIndex += 8) {
int dualbyte = alphabet.IndexOf(bytes[bitIndex / 5]) << 10;
if (bitIndex / 5 + 1 < bytes.Length)
dualbyte |= alphabet.IndexOf(bytes[bitIndex / 5 + 1]) << 5;
if (bitIndex / 5 + 2 < bytes.Length)
dualbyte |= alphabet.IndexOf(bytes[bitIndex / 5 + 2]);
dualbyte = 0xff & (dualbyte >> (15 - bitIndex % 5 - 8));
output.Add((byte)(dualbyte));
}
return output.ToArray();
}
I have come up with my own generic Base32 encoder/decoder implementation for VB.NET. I have verified the results through independent web sites so it does appear to be quite accurate.
Any comments on how improvements could be made to the code will be welcomed.
Option Compare Text
Imports System.ComponentModel
Public Structure Base32(Of T)
Private Const csValidStandardBase32Chars As String = "0123456789ABCDEFGHIJKLMNOPQRSTUV"
<EditorBrowsable(EditorBrowsableState.Never)> _
Class Base32Nibble
<EditorBrowsable(EditorBrowsableState.Never)> _
Friend mStore As New BitArray(5, False)
Public ReadOnly Property Value As Byte
Get
Dim result As Byte = 0
For index As Byte = 0 To mStore.Count - 1
If mStore(index) Then
result += (2 ^ index)
End If
Next
Return result
End Get
End Property
Public Overrides Function ToString() As String
Dim nibbleString As String = Nothing
For Each bit As Boolean In mStore
nibbleString = Math.Abs(CInt(bit)).ToString() & nibbleString
Next
Return nibbleString
End Function
End Class
Private Shared mNibbles As List(Of Base32Nibble)
Public ReadOnly Property Count As Long
Get
Return mNibbles.Count
End Get
End Property
Default Public ReadOnly Property Item(ByVal index As Integer) As Base32Nibble
Get
Return DirectCast(mNibbles(index), Base32Nibble)
End Get
End Property
Public Sub New(ByVal Value As T)
Dim temp As Object = CType(Value, T)
getNibbles(BitConverter.GetBytes(temp))
End Sub
Public Sub New(ByVal Value As Byte())
getNibbles(Value)
End Sub
Public Shared Widening Operator CType(ByVal Value As T) As Base32(Of T)
Return New Base32(Of T)(Value)
End Operator
Public Shared Widening Operator CType(ByVal Value As Byte()) As Base32(Of T)
Return New Base32(Of T)(Value)
End Operator
Public ReadOnly Property Value As String
Get
Dim result As String = Nothing
For Each Nib As Base32(Of T).Base32Nibble In mNibbles
result = csValidStandardBase32Chars(Nib.Value) & result
Next
Return result.TrimStart("0")
End Get
End Property
Public Function ToNumeric(ByVal Base32String As String) As T
Dim result As T = CType(CType(0, Object), T)
Try
If Base32String.Trim.Length > 0 Then
Dim pos As Integer = 0
Do
Dim temp As Object = getBase32Value(Base32String, pos)
result = result + temp
pos += 1
Loop While (pos < Base32String.Length)
End If
Catch ex As Exception
' Catch overflow errors if the generic type T doesn't have enough
' room to store the result
System.Diagnostics.Debug.Print(ex.Message)
End Try
Return result
End Function
Private Shared Sub getNibbles(ByVal Value As Byte())
Dim valueBytes As New BitArray(Value)
Dim nib As Base32Nibble = Nothing
mNibbles = New List(Of Base32Nibble)
Dim padding As Byte = (1 - (valueBytes.Length / 5 - (valueBytes.Length \ 5))) * 5
valueBytes.Length = valueBytes.Length + padding
For element As Short = 0 To valueBytes.Count - 1
If (element Mod 5 = 0) Then
nib = New Base32Nibble()
mNibbles.Add(nib)
End If
nib.mStore.Item(element Mod 5) = valueBytes.Item(element)
Next
End Sub
Private Function getBase32Char(ByVal InputString As String, ByVal InputPosition As Integer) As String
Return csValidStandardBase32Chars.IndexOf(Mid(InputString, InputPosition + 1, 1))
End Function
Private Function getBase32Value(ByVal InputString As String, ByVal InputPosition As Integer) As T
Return CType(CType((getBase32Char(InputString, InputPosition) * (32 ^ (InputString.Length - 1 - InputPosition))), Object), T)
End Function
End Structure
Here is an example of converting 123456789 to Base32
Dim value As Base32(Of Int64) = 123456789
Console.WriteLine( "123456789 in Base32 = " & value.Value)
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