File size: 5,989 Bytes
b1b3bae | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 | Imports System.Text
Imports System.Security.Cryptography
Imports System.IO
Imports System.Linq
Namespace EncryptString
Public NotInheritable Class StringCipher
Private Sub New()
End Sub
' This constant is used to determine the keysize of the encryption algorithm in bits.
' We divide this by 8 within the code below to get the equivalent number of bytes.
Private Const Keysize As Integer = 256
' This constant determines the number of iterations for the password bytes generation function.
Private Const DerivationIterations As Integer = 1000
Public Shared Function Encrypt(plainText As String, passPhrase As String, Optional ByVal encoding As Encoding = Nothing) As String
' Salt and IV is randomly generated each time, but is preprended to encrypted cipher text
' so that the same Salt and IV values can be used when decrypting.
Dim saltStringBytes = Generate256BitsOfRandomEntropy()
Dim ivStringBytes = Generate256BitsOfRandomEntropy()
Dim plainTextBytes As Byte()
If encoding Is Nothing Then
plainTextBytes = Encoding.UTF8.GetBytes(plainText)
Else
plainTextBytes = encoding.GetBytes(plainText)
End If
Using password = New Rfc2898DeriveBytes(passPhrase, saltStringBytes, DerivationIterations)
Dim keyBytes = password.GetBytes(Keysize / 8)
Using symmetricKey = New RijndaelManaged()
symmetricKey.BlockSize = 256
symmetricKey.Mode = CipherMode.CBC
symmetricKey.Padding = PaddingMode.PKCS7
Using encryptor = symmetricKey.CreateEncryptor(keyBytes, ivStringBytes)
Using memoryStream = New MemoryStream()
Using cryptoStream = New CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write)
cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length)
cryptoStream.FlushFinalBlock()
' Create the final bytes as a concatenation of the random salt bytes, the random iv bytes and the cipher bytes.
Dim cipherTextBytes = saltStringBytes
cipherTextBytes = cipherTextBytes.Concat(ivStringBytes).ToArray()
cipherTextBytes = cipherTextBytes.Concat(memoryStream.ToArray()).ToArray()
memoryStream.Close()
cryptoStream.Close()
Return Convert.ToBase64String(cipherTextBytes)
End Using
End Using
End Using
End Using
End Using
End Function
Public Shared Function Decrypt(cipherText As String, passPhrase As String, Optional ByVal encoding As Encoding = Nothing) As String
' Get the complete stream of bytes that represent:
' [32 bytes of Salt] + [32 bytes of IV] + [n bytes of CipherText]
Dim cipherTextBytesWithSaltAndIv = Convert.FromBase64String(cipherText)
' Get the saltbytes by extracting the first 32 bytes from the supplied cipherText bytes.
Dim saltStringBytes = cipherTextBytesWithSaltAndIv.Take(Keysize / 8).ToArray()
' Get the IV bytes by extracting the next 32 bytes from the supplied cipherText bytes.
Dim ivStringBytes = cipherTextBytesWithSaltAndIv.Skip(Keysize / 8).Take(Keysize / 8).ToArray()
' Get the actual cipher text bytes by removing the first 64 bytes from the cipherText string.
Dim cipherTextBytes = cipherTextBytesWithSaltAndIv.Skip((Keysize / 8) * 2).Take(cipherTextBytesWithSaltAndIv.Length - ((Keysize / 8) * 2)).ToArray()
Using password = New Rfc2898DeriveBytes(passPhrase, saltStringBytes, DerivationIterations)
Dim keyBytes = password.GetBytes(Keysize / 8)
Using symmetricKey = New RijndaelManaged()
symmetricKey.BlockSize = 256
symmetricKey.Mode = CipherMode.CBC
symmetricKey.Padding = PaddingMode.PKCS7
Using decryptor = symmetricKey.CreateDecryptor(keyBytes, ivStringBytes)
Using memoryStream = New MemoryStream(cipherTextBytes)
Using cryptoStream = New CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read)
Dim plainTextBytes = New Byte(cipherTextBytes.Length - 1) {}
Dim decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length)
memoryStream.Close()
cryptoStream.Close()
If encoding Is Nothing Then
Return Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount)
Else
Return encoding.GetString(plainTextBytes, 0, decryptedByteCount)
End If
End Using
End Using
End Using
End Using
End Using
End Function
Private Shared Function Generate256BitsOfRandomEntropy() As Byte()
Dim randomBytes = New Byte(31) {}
' 32 Bytes will give us 256 bits.
Using rngCsp = New RNGCryptoServiceProvider()
' Fill the array with cryptographically secure random bytes.
rngCsp.GetBytes(randomBytes)
End Using
Return randomBytes
End Function
End Class
End Namespace
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