How to Convert a Hex String to a Byte Array

How can I convert a hex string to a byte array?

Here's a nice fun LINQ example.

public static byte[] StringToByteArray(string hex) {
    return Enumerable.Range(0, hex.Length)
                     .Where(x => x % 2 == 0)
                     .Select(x => Convert.ToByte(hex.Substring(x, 2), 16))
                     .ToArray();
}

hexadecimal string to byte array in python

Suppose your hex string is something like

>>> hex_string = "deadbeef"

Convert it to a bytearray (Python 3 and 2.7):

>>> bytearray.fromhex(hex_string)
bytearray(b'\xde\xad\xbe\xef')

Convert it to a bytes object (Python 3):

>>> bytes.fromhex(hex_string)
b'\xde\xad\xbe\xef'

Note that bytes is an immutable version of bytearray.

Convert it to a string (Python ≤ 2.7):

>>> hex_data = hex_string.decode("hex")
>>> hex_data
"\xde\xad\xbe\xef"

Convert a string representation of a hex dump to a byte array using Java?

Update (2021) - Java 17 now includes java.util.HexFormat (only took 25 years):

HexFormat.of().parseHex(s)

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For older versions of Java:

Here's a solution that I think is better than any posted so far:

/* s must be an even-length string. */
public static byte[] hexStringToByteArray(String s) {
    int len = s.length();
    byte[] data = new byte[len / 2];
    for (int i = 0; i < len; i += 2) {
        data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                             + Character.digit(s.charAt(i+1), 16));
    }
    return data;
}

Reasons why it is an improvement:

• Safe with leading zeros (unlike BigInteger) and with negative byte values (unlike Byte.parseByte)

• Doesn't convert the String into a char[], or create StringBuilder and String objects for every single byte.

• No library dependencies that may not be available

Feel free to add argument checking via assert or exceptions if the argument is not known to be safe.

Hex String To Byte Array C#

I believe you can use Convert.ToByte(), you might have to slice your string in pairs and loop through it.

If you do a quick search there are many topics on this already on stackoverflow

How do you convert Byte Array to Hexadecimal String, and vice versa?

You can also look at this MS example, it is to convert to int, but the idea is the same.
http://msdn.microsoft.com/en-us/library/bb311038.aspx

C# Convert Hex String Array to Byte Array

You have to convert (or parse) string in order to get byte since string and byte are different types:

// 10 == 10d 
byte b = Convert.ToByte("10");     // if "10" is a decimal representation
// 16 == 0x10
byte b = Convert.ToByte("10", 16); // if "10" is a hexadecimal representation

If you want to process an array, you can try a simple Linq:

using System.Linq;

...

string[] hexValues = new string[] {
  "10", "0F", "3E", "42"};

byte[] result = hexValues
  .Select(value => Convert.ToByte(value, 16))
  .ToArray();

If you want to print out result as hexadecimal, use formatting ("X2" format string - at least 2 hexadecimal digits, use captital letters):

// 10, 0F, 3E, 42
Console.Write(string.Join(", ", result.Select(b => b.ToString("X2")))); 

Compare with same array but in a different format ("d2" - at least 2 decimal digits)

// 16, 15, 62, 66 
Console.Write(string.Join(", ", result.Select(b => b.ToString("d2")))); 

If no format provided, .Net uses default one and represents byte in decimal:

// 16, 15, 62, 66 
Console.Write(string.Join(", ", result));

Converting a hex string to a byte array

This ought to work:

int char2int(char input)
{
  if(input >= '0' && input <= '9')
    return input - '0';
  if(input >= 'A' && input <= 'F')
    return input - 'A' + 10;
  if(input >= 'a' && input <= 'f')
    return input - 'a' + 10;
  throw std::invalid_argument("Invalid input string");
}

// This function assumes src to be a zero terminated sanitized string with
// an even number of [0-9a-f] characters, and target to be sufficiently large
void hex2bin(const char* src, char* target)
{
  while(*src && src[1])
  {
    *(target++) = char2int(*src)*16 + char2int(src[1]);
    src += 2;
  }
}

Depending on your specific platform there's probably also a standard implementation though.

How to convert hex string into a bytes array, and a bytes array in the hex string?

Update: Scroll down for solution... Live Demo

The issue: you are using a lossy conversion to hex, which cannot be reversed.

var p = parseHexString(createHexString(rsa_privk[0]));

This will never be same as rsa_privk[0].

Because, createHexString() only uses the last 2 bytes from each array element.

Example:

rsa_privk[0] : [123676133, 198914513, 129998601, 245147334, 11918451, 206998232, 96766191, 75984899, 177840095, 106709334, 10180427, 208237547, 119814814, 127003446, 189062377, 84099480, 220452154, 250519075, 267883908, 115471915, 165124106, 238628722, 169382478, 42320122, 95982405, 80725759, 89608310, 85166267, 200925925, 254033325, 86971506, 191278317, 127411298, 180195794, 142776693, 188738169, 39016]

createHexString(rsa_privk[0]) : e5d109c673d8ef03df564beb9e36e9983a23842b0a724efa45ff76bbe5ad72ed62d2757968

parseHexString(createHexString(rsa_privk[0])) : [229, 209, 9, 198, 115, 216, 239, 3, 223, 86, 75, 235, 158, 54, 233, 152, 58, 35, 132, 43, 10, 114, 78, 250, 69, 255, 118, 187, 229, 173, 114, 237, 98, 210, 117, 121, 104] 

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Update : Working Solution...

The two functions... the hex always contains 8 byte blocks, each for each element in the array...

function parseHexString(str) { 
    var result = [];
    while (str.length >= 8) { 
        result.push(parseInt(str.substring(0, 8), 16));

        str = str.substring(8, str.length);
    }

    return result;
}

function createHexString(arr) {
    var result = "";
    var z;

    for (var i = 0; i < arr.length; i++) {
        var str = arr[i].toString(16);

        z = 8 - str.length + 1;
        str = Array(z).join("0") + str;

        result += str;
    }

    return result;
}

Test code...

function test() {   
    a = [123676133, 198914513, 129998601, 245147334, 11918451, 206998232, 96766191, 75984899, 177840095, 106709334, 10180427, 208237547, 119814814, 127003446, 189062377, 84099480, 220452154, 250519075, 267883908, 115471915, 165124106, 238628722, 169382478, 42320122, 95982405, 80725759, 89608310, 85166267, 200925925, 254033325, 86971506, 191278317, 127411298, 180195794, 142776693, 188738169, 39016];

    console.log("Input");
    console.log(a);

    b = createHexString(a);

    console.log("Hex");
    console.log(b);

    c = parseHexString(b); 

    console.log("Output");
    console.log(c);

    if(checkIfEqual(a, c)) {
        alert("Same");
    }
}

function checkIfEqual(arr1, arr2) {
    if (arr1.length != arr2.length) {
        return false;
    }
    //sort them first, then join them and just compare the strings
    return arr1.sort().join() == arr2.sort().join();
}

C# - Convert hex string to byte array of hex values

string hexIpAddress = "0A010248"; // 10.1.2.72 => "0A010248"
byte[] bytes = new byte[hexIpAddress.Length / 2];

for (int i = 0; i < hexIpAddress.Length; i += 2)
    bytes[i/2] = Convert.ToByte(hexIpAddress.Substring(i, 2), 16);

This results in this array:

bytes = {0x0A, 0x01, 0x02, 0x48}; 

or represented as decimals:

bytes = {10, 1, 2, 72};

or as binaries 00001010, 000000001, 00000010, 01001000 (binary literals are still not supported in C#6).

The values are the same, there is no representation in any base in byte. You can only decide how the values should be represented when converting them to strings again:

foreach(byte b in bytes)
    Console.WriteLine("{0} {0:X}", b);

results in

10 A
1 1
2 2
72 48

Hexadecimal string to byte array in C

As far as I know, there's no standard function to do so, but it's simple to achieve in the following manner:

#include <stdio.h>

int main(int argc, char **argv) {
    const char hexstring[] = "DEadbeef10203040b00b1e50", *pos = hexstring;
    unsigned char val[12];

     /* WARNING: no sanitization or error-checking whatsoever */
    for (size_t count = 0; count < sizeof val/sizeof *val; count++) {
        sscanf(pos, "%2hhx", &val[count]);
        pos += 2;
    }

    printf("0x");
    for(size_t count = 0; count < sizeof val/sizeof *val; count++)
        printf("%02x", val[count]);
    printf("\n");

    return 0;
}

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Edit

As Al pointed out, in case of an odd number of hex digits in the string, you have to make sure you prefix it with a starting 0. For example, the string "f00f5" will be evaluated as {0xf0, 0x0f, 0x05} erroneously by the above example, instead of the proper {0x0f, 0x00, 0xf5}.

Amended the example a little bit to address the comment from @MassimoCallegari

Convert hex string to byte []

Convert hex to byte and byte to hex.

public static byte[] hexStringToByteArray(String s) {
                int len = s.length();
                byte[] data = new byte[len/2];

                for(int i = 0; i < len; i+=2){
                    data[i/2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) + Character.digit(s.charAt(i+1), 16));
                }

                return data;
            }

final protected static char[] hexArray = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
public static String byteArrayToHexString(byte[] bytes) {
            char[] hexChars = new char[bytes.length*2];
            int v;

            for(int j=0; j < bytes.length; j++) {
                v = bytes[j] & 0xFF;
                hexChars[j*2] = hexArray[v>>>4];
                hexChars[j*2 + 1] = hexArray[v & 0x0F];
            }

            return new String(hexChars);
        }

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