Develop Reference

My symmetric encryption adds data to my rsa key I want to save and load encrypted

Currently I am trying to implement a save function for my RSA key with the help of bouncycastle. I am running into problems if I try to save my public or private key encrypted and load it afterwards.
As a little example here the original public key:
305C300D06092A864886F70D0101010500034B00304802410096B4751049165D1E046063EA22E8FFA0F90AE1DD997A3876DA5F79C7DE97951F009AC9ACA3EB91114F8A32C04F48293B6665CD6DD5C406C81CD13270A2AB61130203010001
What I get after loading it (it adds 4 zeroes, bigger key means more zeroes added):
305C300D06092A864886F70D0101010500034B00304802410096B4751049165D1E046063EA22E8FFA0F90AE1DD997A3876DA5F79C7DE97951F009AC9ACA3EB91114F8A32C04F48293B6665CD6DD5C406C81CD13270A2AB611302030100010000
I found out it has something to do with my implementation of the symmetric encryption and the padding used there. Normal text no matter how long it is just works fine without extra data getting added.
This is the code I am using for my AES encryption:
Encryption
byte[] outputBytes = new byte[0];
AesEngine aesengine = new AesEngine();
CbcBlockCipher aesblockCipher = new CbcBlockCipher(aesengine);
PaddedBufferedBlockCipher aescipher = new PaddedBufferedBlockCipher(aesblockCipher);
KeyParameter aeskeyParameter = new KeyParameter(Hash.HashDataBlock(password, Hash.HashAlgorithm.SHA3).Bytes);
aescipher.Init(true, aeskeyParameter);
outputBytes = new byte[aescipher.GetOutputSize(inputBytes.Bytes.Length)];
int aeslength = aescipher.ProcessBytes(inputBytes.Bytes, outputBytes, 0);
aescipher.DoFinal(outputBytes, aeslength);
Decryption
byte[] inputBytes = input.Bytes;
byte[] outputBytes = new byte[0];
AesEngine aesengine = new AesEngine();
CbcBlockCipher aesblockCipher = new CbcBlockCipher(aesengine);
PaddedBufferedBlockCipher aescipher = new PaddedBufferedBlockCipher(aesblockCipher);
KeyParameter aeskeyParameter = new KeyParameter(Hash.HashDataBlock(password, Hash.HashAlgorithm.SHA3).Bytes);
aescipher.Init(false, aeskeyParameter);
outputBytes = new byte[aescipher.GetOutputSize(inputBytes.Length)];
int aeslength = aescipher.ProcessBytes(inputBytes, outputBytes, 0);
aescipher.DoFinal(outputBytes, aeslength);
My Functions to save and load the keys. The DataBlock class just converts data to needed formats like UTF8, Base64 or just byte arrays:
public static void SaveKeyEncrypted(DataBlock key, string path, DataBlock password)
{
StreamWriter sw = new StreamWriter(path);
DataBlock encrypted = SymmetricEncryption.Encrypt(key, password, SymmetricEncryption.SymmetricAlgorithms.AES);
sw.Write(encrypted.Base64);
sw.Close();
}
public static DataBlock ReadKeyEncrypted(string path, DataBlock password)
{
StreamReader sr = new StreamReader(path);
DataBlock readData = new DataBlock(sr.ReadLine(), DataBlock.DataType.Base64);
sr.Close();
return SymmetricEncryption.Decrypt(readData, password, SymmetricEncryption.SymmetricAlgorithms.AES);
}
For reproduction my other code that has to do with this problem:
public class DataBlock
{
private byte[] _data;
public DataBlock()
{
this._data = new byte[0];
}
public enum DataType
{
UTF8,
UTF7,
UTF32,
ASCII,
Unicode,
Hex,
Base64,
Base32
}
public DataBlock(string data, DataType dataType) : this()
{
switch (dataType)
{
case DataType.UTF8:
this._data = Encoding.UTF8.GetBytes(data);
break;
case DataType.UTF7:
this._data = Encoding.UTF7.GetBytes(data);
break;
case DataType.UTF32:
this._data = Encoding.UTF32.GetBytes(data);
break;
case DataType.ASCII:
this._data = Encoding.ASCII.GetBytes(data);
break;
case DataType.Unicode:
this._data = Encoding.Unicode.GetBytes(data);
break;
case DataType.Hex:
this._data = new byte[data.Length / 2];
for (int i = 0; i < data.Length; i += 2)
{
this._data[i / 2] = Convert.ToByte(data.Substring(i, 2), 16);
}
break;
case DataType.Base64:
this._data = Convert.FromBase64String(data);
break;
case DataType.Base32:
this._data = this.FromBase32String(data);
break;
}
}
public DataBlock(byte[] data)
{
this._data = data;
}
public string UTF8
{
get
{
return Encoding.UTF8.GetString(this._data);
}
}
public string UTF7
{
get
{
return Encoding.UTF7.GetString(this._data);
}
}
public string UTF32
{
get
{
return Encoding.UTF32.GetString(this._data);
}
}
public string ASCII
{
get
{
return Encoding.ASCII.GetString(this._data);
}
}
public string Unicode
{
get
{
return Encoding.Unicode.GetString(this._data);
}
}
public string Hex
{
get
{
return BitConverter.ToString(this._data).Replace("-", "");
}
}
public string Base64
{
get
{
return Convert.ToBase64String(this._data);
}
}
public string Base32
{
get
{
return this.ToBase32String(this._data);
}
}
public byte[] Bytes
{
get
{
return this._data;
}
}
private string ValidChars = "QAZ2WSX3" + "EDC4RFV5" + "TGB6YHN7" + "UJM8K9LP";
private string ToBase32String(byte[] bytes)
{
StringBuilder sb = new StringBuilder();
byte index;
int hi = 5;
int currentByte = 0;
while (currentByte < bytes.Length)
{
if (hi > 8)
{
index = (byte)(bytes[currentByte++] >> (hi - 5));
if (currentByte != bytes.Length)
{
index = (byte)(((byte)(bytes[currentByte] << (16 - hi)) >> 3) | index);
}
hi -= 3;
}
else if (hi == 8)
{
index = (byte)(bytes[currentByte++] >> 3);
hi -= 3;
}
else
{
index = (byte)((byte)(bytes[currentByte] << (8 - hi)) >> 3);
hi += 5;
}
sb.Append(ValidChars[index]);
}
return sb.ToString();
}
public byte[] FromBase32String(string str)
{
int numBytes = str.Length * 5 / 8;
byte[] bytes = new Byte[numBytes];
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;
}
}
Function to generate a keypair
public static DataBlock[] GenerateKeyPair(KeyPairSize keyPairSize)
{
RsaKeyPairGenerator keyPairGenerator = new RsaKeyPairGenerator();
keyPairGenerator.Init(new KeyGenerationParameters(new SecureRandom(new CryptoApiRandomGenerator()), (int) keyPairSize));
AsymmetricCipherKeyPair keyPair = keyPairGenerator.GenerateKeyPair();
PrivateKeyInfo pkInfo = PrivateKeyInfoFactory.CreatePrivateKeyInfo(keyPair.Private);
SubjectPublicKeyInfo info = SubjectPublicKeyInfoFactory.CreateSubjectPublicKeyInfo(keyPair.Public);
DataBlock[] keyPairData = new DataBlock[2];
keyPairData[0] = new DataBlock(pkInfo.GetDerEncoded());
keyPairData[1] = new DataBlock(info.GetDerEncoded());
return keyPairData;
}
Code to reproduce the error:
DataBlock[] keyPair = AsymmetricEncryption.GenerateKeyPair(AsymmetricEncryption.KeyPairSize.Bits512);
DataBlock pass = new DataBlock("1234", DataBlock.DataType.UTF8);
DataBlock orig = new DataBlock("Hello World", DataBlock.DataType.UTF8);
DataBlock encrypted = AsymmetricEncryption.Encrypt(orig, keyPair[1]);
AsymmetricEncryption.SaveKeyEncrypted(keyPair[0], "D:\\privateenc", pass);
AsymmetricEncryption.SaveKeyEncrypted(keyPair[1], "D:\\publicenc", pass);
DataBlock privateKey = AsymmetricEncryption.ReadKeyEncrypted("D:\\privateenc", pass);
DataBlock publicKey = AsymmetricEncryption.ReadKeyEncrypted("D:\\publicenc", pass);
DataBlock decrypted = AsymmetricEncryption.Decrypt(encrypted, privateKey);
Console.WriteLine(decrypted.UTF8);
The encryption/decryption method is not needed because the error already happens after reading the encrypted key on my harddrive.
Why/where is the extra data added and how can I fix it?

I was able to fix it by adding the initial byte array length of the key to the encrypted text and read it later on. In the read function I cut everything after the original size of the key.
The main problem is still present and this is just a workaround.

Problem with base 64 encoding and decoding [duplicate]

How do I return a base64 encoded string given a string?
How do I decode a base64 encoded string into a string?

Encode
public static string Base64Encode(string plainText)
{
var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(plainText);
return System.Convert.ToBase64String(plainTextBytes);
}
Decode
public static string Base64Decode(string base64EncodedData)
{
var base64EncodedBytes = System.Convert.FromBase64String(base64EncodedData);
return System.Text.Encoding.UTF8.GetString(base64EncodedBytes);
}

One liner code:
Note: Use System and System.Text directives.
Encode:
string encodedStr = Convert.ToBase64String(Encoding.UTF8.GetBytes("inputStr"));
Decode:
string inputStr = Encoding.UTF8.GetString(Convert.FromBase64String(encodedStr));

I'm sharing my implementation with some neat features:
uses Extension Methods for Encoding class. Rationale is that someone may need to support different types of encodings (not only UTF8).
Another improvement is failing gracefully with null result for null entry - it's very useful in real life scenarios and supports equivalence for X=decode(encode(X)).
Remark: Remember that to use Extension Method you have to (!) import the namespace with using keyword (in this case using MyApplication.Helpers.Encoding).
Code:
namespace MyApplication.Helpers.Encoding
{
public static class EncodingForBase64
{
public static string EncodeBase64(this System.Text.Encoding encoding, string text)
{
if (text == null)
{
return null;
}
byte[] textAsBytes = encoding.GetBytes(text);
return System.Convert.ToBase64String(textAsBytes);
}
public static string DecodeBase64(this System.Text.Encoding encoding, string encodedText)
{
if (encodedText == null)
{
return null;
}
byte[] textAsBytes = System.Convert.FromBase64String(encodedText);
return encoding.GetString(textAsBytes);
}
}
}
Usage example:
using MyApplication.Helpers.Encoding; // !!!
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
Test1();
Test2();
}
static void Test1()
{
string textEncoded = System.Text.Encoding.UTF8.EncodeBase64("test1...");
System.Diagnostics.Debug.Assert(textEncoded == "dGVzdDEuLi4=");
string textDecoded = System.Text.Encoding.UTF8.DecodeBase64(textEncoded);
System.Diagnostics.Debug.Assert(textDecoded == "test1...");
}
static void Test2()
{
string textEncoded = System.Text.Encoding.UTF8.EncodeBase64(null);
System.Diagnostics.Debug.Assert(textEncoded == null);
string textDecoded = System.Text.Encoding.UTF8.DecodeBase64(textEncoded);
System.Diagnostics.Debug.Assert(textDecoded == null);
}
}
}

Based on the answers by Andrew Fox and Cebe, I turned it around and made them string extensions instead of Base64String extensions.
public static class StringExtensions
{
public static string ToBase64(this string text)
{
return ToBase64(text, Encoding.UTF8);
}
public static string ToBase64(this string text, Encoding encoding)
{
if (string.IsNullOrEmpty(text))
{
return text;
}
byte[] textAsBytes = encoding.GetBytes(text);
return Convert.ToBase64String(textAsBytes);
}
public static bool TryParseBase64(this string text, out string decodedText)
{
return TryParseBase64(text, Encoding.UTF8, out decodedText);
}
public static bool TryParseBase64(this string text, Encoding encoding, out string decodedText)
{
if (string.IsNullOrEmpty(text))
{
decodedText = text;
return false;
}
try
{
byte[] textAsBytes = Convert.FromBase64String(text);
decodedText = encoding.GetString(textAsBytes);
return true;
}
catch (Exception)
{
decodedText = null;
return false;
}
}
}

A slight variation on andrew.fox answer, as the string to decode might not be a correct base64 encoded string:
using System;
namespace Service.Support
{
public static class Base64
{
public static string ToBase64(this System.Text.Encoding encoding, string text)
{
if (text == null)
{
return null;
}
byte[] textAsBytes = encoding.GetBytes(text);
return Convert.ToBase64String(textAsBytes);
}
public static bool TryParseBase64(this System.Text.Encoding encoding, string encodedText, out string decodedText)
{
if (encodedText == null)
{
decodedText = null;
return false;
}
try
{
byte[] textAsBytes = Convert.FromBase64String(encodedText);
decodedText = encoding.GetString(textAsBytes);
return true;
}
catch (Exception)
{
decodedText = null;
return false;
}
}
}
}

You can use below routine to convert string to base64 format
public static string ToBase64(string s)
{
byte[] buffer = System.Text.Encoding.Unicode.GetBytes(s);
return System.Convert.ToBase64String(buffer);
}
Also you can use very good online tool OnlineUtility.in to encode string in base64 format

URL safe Base64 Encoding/Decoding
public static class Base64Url
{
public static string Encode(string text)
{
return Convert.ToBase64String(Encoding.UTF8.GetBytes(text)).TrimEnd('=').Replace('+', '-')
.Replace('/', '_');
}
public static string Decode(string text)
{
text = text.Replace('_', '/').Replace('-', '+');
switch (text.Length % 4)
{
case 2:
text += "==";
break;
case 3:
text += "=";
break;
}
return Encoding.UTF8.GetString(Convert.FromBase64String(text));
}
}

// Encoding
string passw = "tes123";
var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(passw);
string pass = System.Convert.ToBase64String(plainTextBytes);
// Normal
var encodedTextBytes = Convert.FromBase64String(pass);
string plainText = Encoding.UTF8.GetString(encodedTextBytes);

using System;
using System.Text;
public static class Base64Conversions
{
public static string EncodeBase64(this string text, Encoding encoding = null)
{
if (text == null) return null;
encoding = encoding ?? Encoding.UTF8;
var bytes = encoding.GetBytes(text);
return Convert.ToBase64String(bytes);
}
public static string DecodeBase64(this string encodedText, Encoding encoding = null)
{
if (encodedText == null) return null;
encoding = encoding ?? Encoding.UTF8;
var bytes = Convert.FromBase64String(encodedText);
return encoding.GetString(bytes);
}
}
Usage
var text = "Sample Text";
var base64 = text.EncodeBase64();
base64 = text.EncodeBase64(Encoding.UTF8); //or with Encoding

For those that simply want to encode/decode individual base64 digits:
public static int DecodeBase64Digit(char digit, string digit62 = "+-.~", string digit63 = "/_,")
{
if (digit >= 'A' && digit <= 'Z') return digit - 'A';
if (digit >= 'a' && digit <= 'z') return digit + (26 - 'a');
if (digit >= '0' && digit <= '9') return digit + (52 - '0');
if (digit62.IndexOf(digit) > -1) return 62;
if (digit63.IndexOf(digit) > -1) return 63;
return -1;
}
public static char EncodeBase64Digit(int digit, char digit62 = '+', char digit63 = '/')
{
digit &= 63;
if (digit < 52)
return (char)(digit < 26 ? digit + 'A' : digit + ('a' - 26));
else if (digit < 62)
return (char)(digit + ('0' - 52));
else
return digit == 62 ? digit62 : digit63;
}
There are various versions of Base64 that disagree about what to use for digits 62 and 63, so DecodeBase64Digit can tolerate several of these.

You can display it like this:
var strOriginal = richTextBox1.Text;
byte[] byt = System.Text.Encoding.ASCII.GetBytes(strOriginal);
// convert the byte array to a Base64 string
string strModified = Convert.ToBase64String(byt);
richTextBox1.Text = "" + strModified;
Now, converting it back.
var base64EncodedBytes = System.Convert.FromBase64String(richTextBox1.Text);
richTextBox1.Text = "" + System.Text.Encoding.ASCII.GetString(base64EncodedBytes);
MessageBox.Show("Done Converting! (ASCII from base64)");
I hope this helps!

To encode a string into a base64 string in C#, you can use the Convert.ToBase64String method:
string originalString = "Hello World";
string encodedString = Convert.ToBase64String(Encoding.UTF8.GetBytes(originalString));
To decode a base64 encoded string into a string in C#, you can use the Convert.FromBase64String method:
string encodedString = "SGVsbG8gV29ybGQ=";
string originalString = Encoding.UTF8.GetString(Convert.FromBase64String(encodedString));

Binary to string/string to binary

I want to convert text into binary and after that, to try convert binary into string text.
How can i convert tobin back into text if it is already a string?
private void iTalk_Button_12_Click(object sender, EventArgs e)
{
ambiance_RichTextBox2.Text = tobin(ambiance_RichTextBox1.Text);
}
public string tobin(string inp)
{
StringBuilder sb = new StringBuilder();
foreach (char L in inp.ToCharArray())
{
sb.Append(Convert.ToString(L, 2).PadLeft(8, '0'));
}
return sb.ToString();
}

private void iTalk_Button_12_Click(object sender, EventArgs e)
{
ambiance_RichTextBox2.Text = BinaryToString(ambiance_RichTextBox1.Text);
//use what u need: BinaryToString or StringToBinary.
}
Convert String to Binary:
public static string StringToBinary(string data)
{
StringBuilder sb = new StringBuilder();
foreach (char c in data.ToCharArray())
{
sb.Append(Convert.ToString(c, 2).PadLeft(8, '0'));
}
return sb.ToString();
}
Convert Binary to String:
public static string BinaryToString(string data)
{
List<Byte> byteList = new List<Byte>();
for (int i = 0; i < data.Length; i += 8)
{
byteList.Add(Convert.ToByte(data.Substring(i, 8), 2));
}
return Encoding.ASCII.GetString(byteList.ToArray());
}
Good luck!

You can use like this,
public static string BinaryToString(string data)
{
List<Byte> byteList = new List<Byte>();
for (int i = 0; i < data.Length; i += 8)
{
byteList.Add(Convert.ToByte(data.Substring(i, 8), 2));
}
return Encoding.ASCII.GetString(byteList.ToArray());
}

Currently you are converting a char (which can be represented as a number) to its binary representation (this number is the ASCII number). But if you want to convert a string to binary, you should use an encoding. The encoding determines how the text is converted to binary.
For example:
static void Main(string[] args)
{
string input = "This is an example text.";
Console.WriteLine(input);
string asBin = ToBinary(input);
Console.WriteLine(asBin);
string asText = ToText(asBin);
Console.WriteLine(asText);
}
static string ToBinary(string input, System.Text.Encoding encoding = null)
{
if (encoding == null)
encoding = System.Text.Encoding.UTF8;
var builder = new System.Text.StringBuilder();
var bytes = encoding.GetBytes(input); // Convert the text to bytes using the encoding
foreach (var b in bytes)
builder.Append(Convert.ToString(b, 2).PadLeft(8, '0')); //Convert the byte to its binary representation
return builder.ToString();
}
static string ToText(string bytes, System.Text.Encoding encoding = null)
{
if (encoding == null)
encoding = System.Text.Encoding.UTF8;
var byteCount = 8;
var byteArray = new byte[bytes.Length / 8]; // An array for the bytes
for (int i = 0; i < bytes.Length / byteCount; i++)
{
var subBytes = bytes.Substring(i * byteCount, byteCount); // Get a subpart of 8 bits
var b = Convert.ToByte(subBytes.TrimStart('0'), 2); // Convert the subpart to a byte
byteArray[i] = b; // Add the byte to the array
}
return encoding.GetString(byteArray); // Convert the array to text using the right encoding.
}
Now if you want to use ASCII encoding, you can call the functions as follows:
Console.WriteLine(input);
string asBin = ToBinary(input, System.Text.Encoding.ASCII);
Console.WriteLine(asBin);
string asText = ToText(asBin, System.Text.Encoding.ASCII);
Console.WriteLine(asText);

To convert a string to binary
string s = "hai";
byte []arr = System.Text.Encoding.ASCII.GetBytes(s);
To convert binary to string
byte[] arr ;
string s = Encoding.ASCII.GetString(arr);

Binary To Corresponding ASCII String Conversion

Hi i was able to convert a ASCII string to binary using a binarywriter .. as 10101011 . im required back to convert Binary ---> ASCII string .. any idea how to do it ?

This should do the trick... or at least get you started...
public Byte[] GetBytesFromBinaryString(String binary)
{
var list = new List<Byte>();
for (int i = 0; i < binary.Length; i += 8)
{
String t = binary.Substring(i, 8);
list.Add(Convert.ToByte(t, 2));
}
return list.ToArray();
}
Once the binary string has been converted to a byte array, finish off with
Encoding.ASCII.GetString(data);
So...
var data = GetBytesFromBinaryString("010000010100001001000011");
var text = Encoding.ASCII.GetString(data);

If you have ASCII charters only you could use Encoding.ASCII.GetBytes and Encoding.ASCII.GetString.
var text = "Test";
var bytes = Encoding.ASCII.GetBytes(text);
var newText = Encoding.ASCII.GetString(bytes);

Here is complete code for your answer
FileStream iFile = new FileStream(#"c:\test\binary.dat",
FileMode.Open);
long lengthInBytes = iFile.Length;
BinaryReader bin = new BinaryReader(aFile);
byte[] byteArray = bin.ReadBytes((int)lengthInBytes);
System.Text.Encoding encEncoder = System.Text.ASCIIEncoding.ASCII;
string str = encEncoder.GetString(byteArray);

Take this as a simple example:
public void ByteToString()
{
Byte[] arrByte = { 0, 1, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0 };
string x = Convert.ToBase64String(arrByte);
}
This linked answer has interesting details about this kind of conversion:
binary file to string

Sometimes instead of using the built in tools it's better to use "custom" code.. try this function:
public string BinaryToString(string binary)
{
if (string.IsNullOrEmpty(binary))
throw new ArgumentNullException("binary");
if ((binary.Length % 8) != 0)
throw new ArgumentException("Binary string invalid (must divide by 8)", "binary");
StringBuilder builder = new StringBuilder();
for (int i = 0; i < binary.Length; i += 8)
{
string section = binary.Substring(i, 8);
int ascii = 0;
try
{
ascii = Convert.ToInt32(section, 2);
}
catch
{
throw new ArgumentException("Binary string contains invalid section: " + section, "binary");
}
builder.Append((char)ascii);
}
return builder.ToString();
}
Tested with 010000010100001001000011 it returned ABC using the "raw" ASCII values.

C# Replace bytes in Byte[]

What is the best way to replace some bytes in a byte array??
For instance i have bytesFromServer = listener.Receive(ref groupEP); and i can do BitConverter.ToString(bytesFromServer) to convert it into a readable format to return something along the lines of
48 65 6c 6c 6f 20
74 68 65 72 65 20
68 65 6c 70 66 75
6c 20 70 65 6f 70
6c 65
I would like to replace something inside of that making "68 65 6c" to something like "68 00 00" (just as an example). There is not .Replace() on a byte[].
Would there be an easy way to convert that back into a byte[]?
Any help appreciated. Thank you!

You could program it.... try this for a start... this is however not robust not production like code yet...beaware of off-by-one errors I didn't fully test this...
public int FindBytes(byte[] src, byte[] find)
{
int index = -1;
int matchIndex = 0;
// handle the complete source array
for(int i=0; i<src.Length; i++)
{
if(src[i] == find[matchIndex])
{
if (matchIndex==(find.Length-1))
{
index = i - matchIndex;
break;
}
matchIndex++;
}
else if (src[i] == find[0])
{
matchIndex = 1;
}
else
{
matchIndex = 0;
}
}
return index;
}
public byte[] ReplaceBytes(byte[] src, byte[] search, byte[] repl)
{
byte[] dst = null;
int index = FindBytes(src, search);
if (index>=0)
{
dst = new byte[src.Length - search.Length + repl.Length];
// before found array
Buffer.BlockCopy(src,0,dst,0, index);
// repl copy
Buffer.BlockCopy(repl,0,dst,index,repl.Length);
// rest of src array
Buffer.BlockCopy(
src,
index+search.Length ,
dst,
index+repl.Length,
src.Length-(index+search.Length));
}
return dst;
}
Implement as an extension method
public void Replace(this byte[] src, byte[] search, byte[] repl)
{
ReplaceBytes(src, search, repl);
}
usage normal method:
ReplaceBytes(bytesfromServer,
new byte[] {0x75, 0x83 } ,
new byte[]{ 0x68, 0x65, 0x6c});
Extension method usage:
bytesfromServer.Replace(
new byte[] {0x75, 0x83 },
new byte[]{ 0x68, 0x65, 0x6c});

Improving on rene's code, I created a while loop for it to replace all occurences:
public static byte[] ReplaceBytes(byte[] src, byte[] search, byte[] repl)
{
byte[] dst = null;
byte[] temp = null;
int index = FindBytes(src, search);
while (index >= 0)
{
if (temp == null)
temp = src;
else
temp = dst;
dst = new byte[temp.Length - search.Length + repl.Length];
// before found array
Buffer.BlockCopy(temp, 0, dst, 0, index);
// repl copy
Buffer.BlockCopy(repl, 0, dst, index, repl.Length);
// rest of src array
Buffer.BlockCopy(
temp,
index + search.Length,
dst,
index + repl.Length,
temp.Length - (index + search.Length));
index = FindBytes(dst, search);
}
return dst;
}
This method will work, but if the source bytes is too huge, I prefer to have a "windowing" function to process the bytes chunk by chunk. Else it will take a huge amount of memory.

How about Array.Copy?

Unfortunately there are issues with all of the posts (as already pointed out in comments). There is a correct answer in this other question
I needed a solution so for myself and wrote the following code. This is also more flexible in using enumerable and multiple search replace terms.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class ByteTools
{
static void ByteReplaceTests()
{
var examples = new(string source, string search, string replace)[]
{
("bababanana", "babanana", "apple"),
("hello guys", "hello", "hello world"),
("apple", "peach", "pear"),
("aaaa", "a", "abc"),
("pear", "pear", ""),
("good morning world", "morning", "morning"),
("ababab", "ab", "ababab"),
("ababab", "abab", "ab"),
("", "aa", "bb"),
};
int i = 0;
foreach (var (source, search, replace) in examples)
{
var stringReplaceResults = source.Replace(search, replace);
var sourceByte = Encoding.ASCII.GetBytes(source);
var searchByte = Encoding.ASCII.GetBytes(search);
var replaceByte = Encoding.ASCII.GetBytes(replace);
//converts string values to bytes, does the replace, then converts back to string
var byteReplaceResults = Encoding.ASCII.GetString(
ByteReplace(sourceByte, (searchByte, replaceByte)).ToArray());
Console.WriteLine($"{i}: {source}, {search}, {replace}");
Console.WriteLine($" String.Replace() => {stringReplaceResults}");
Console.WriteLine($" BytesReplace() => {byteReplaceResults}");
i++;
}
}
static IEnumerable<byte> ByteReplace(IEnumerable<byte> source, params (byte[] search, byte[] replace)[] replacements)
{
if (source == null)
throw new ArgumentNullException(nameof(source));
if (replacements == null)
throw new ArgumentNullException(nameof(replacements));
if (replacements.Any(r => r.search == null || r.search.Length == 0))
throw new ArgumentOutOfRangeException(nameof(replacements), "Search parameter cannot be null or empty");
if (replacements.Any(r => r.replace == null))
throw new ArgumentOutOfRangeException(nameof(replacements), "Replace parameter cannot be null");
var maxMatchSize = replacements.Select(r => r.search.Length).Max();
var bufferSize = maxMatchSize * 2;
var buffer = new byte[bufferSize];
int bufferStart = 0;
int bufferPosition = 0;
byte[] nextBytes()
{
foreach ((byte[] search, byte[] replace) in replacements)
{
if (ByteStartsWith(buffer, bufferStart, bufferPosition - bufferStart, search))
{
bufferStart += search.Length;
return replace;
}
}
var returnBytes = new byte[] { buffer[bufferStart] };
bufferStart++;
return returnBytes;
}
foreach (var dataByte in source)
{
buffer[bufferPosition] = dataByte;
bufferPosition++;
if (bufferPosition - bufferStart >= maxMatchSize)
{
foreach (var resultByte in nextBytes())
yield return resultByte;
}
if (bufferPosition == bufferSize - 1)
{
Buffer.BlockCopy(buffer, bufferStart, buffer, 0, bufferPosition - bufferStart);
bufferPosition -= bufferStart;
bufferStart = 0;
}
}
while (bufferStart < bufferPosition)
{
foreach (var resultByte in nextBytes())
yield return resultByte;
}
}
static bool ByteStartsWith(byte[] data, int dataOffset, int dataLength, byte[] startsWith)
{
if (data == null)
throw new ArgumentNullException(nameof(data));
if (startsWith == null)
throw new ArgumentNullException(nameof(startsWith));
if (dataLength < startsWith.Length)
return false;
for (int i = 0; i < startsWith.Length; i++)
{
if (data[i + dataOffset] != startsWith[i])
return false;
}
return true;
}
}

public static byte[] ReplaceBytes(byte[] src, byte[] search, byte[] repl)
{
if (repl == null) return src;
int index = FindBytes(src, search);
if (index < 0) return src;
byte[] dst = new byte[src.Length - search.Length + repl.Length];
Buffer.BlockCopy(src, 0, dst, 0, index);
Buffer.BlockCopy(repl, 0, dst, index, repl.Length);
Buffer.BlockCopy(src, index + search.Length, dst, index + repl.Length,src.Length - (index + search.Length));
return dst;
}
public static int FindBytes(byte[] src, byte[] find)
{
if(src==null|| find==null|| src.Length==0|| find.Length == 0 || find.Length> src.Length) return -1;
for (int i = 0; i < src.Length - find.Length +1 ; i++)
{
if (src[i] == find[0])
{
for(int m=1;m< find.Length;m++)
{
if (src[i + m] != find[m]) break;
if (m == find.Length - 1) return i;
}
}
}
return -1;
}
this may be a good method , i have test in lots of codes.

Something i pieced together... Going to test it soon. Credits from How do you convert Byte Array to Hexadecimal String, and vice versa?
public byte[] ReplaceBytes(byte[] src, string replace, string replacewith)
{
string hex = BitConverter.ToString(src);
hex = hex.Replace("-", "");
hex = hex.Replace(replace, replacewith);
int NumberChars = hex.Length;
byte[] bytes = new byte[NumberChars / 2];
for (int i = 0; i < NumberChars; i += 2)
bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);
return bytes;
}