.NET Encryption Using SymmetricAlgorithm & Rijndael

2009-05-29T06:38:00.000-07:00

After much research into finding the best way to encrypt and decrypt strings I have come up with a working solution. I have tried other solutions such as one I found on CodeProject that worked sometimes but I would run into the error "Length of the data to decrypt is invalid." this is due to the Public and Private Keys and how they are generated. I have used this sytem to encrypt email body text into a database to secure sensitive information. In this senario the encrypted email data is sent to a centralized MSMQ where it is picked up and logged into a database and then the email is decrypted and sent out. Below is my encryption class that works great.

Imports System

Imports System.Security.Cryptography

Imports System.IO

Imports System.Text

'clsEncryption
is a wrapper of System.Security.Cryptography.SymmetricAlgorithm classes

'and simplifies
the interface. It supports customized SymmetricAlgorithm as well.

Public Class clsEncryption

'================================================================

'MEMBER VARIABLES

'================================================================

Shared encryptionAlgorithm As SymmetricAlgorithm = InitializeEncryptionAlgorithm()

'================================================================

'METHODS

'================================================================

Private Shared Function InitializeEncryptionAlgorithm() As SymmetricAlgorithm

Try

Dim rijaendel As SymmetricAlgorithm = RijndaelManaged.Create()

rijaendel.Key = GetLegalKey("vGCrSnMUBIwJX0+6jc/k2294nmkwWF2fm3B8ImGKqPI=")

rijaendel.IV = New Byte() {&HF, &H6F, &H13, &H2E, &H35, &HC2, &HCD,&HF9,&H5,&H46,&H9C, &HEA, &HA8, &H4B, &H73, &HCC}

Return rijaendel

Catch ex As Exception

Return Nothing

End Try

End Function

Public Function GetKey() As String

Return Convert.ToBase64String(encryptionAlgorithm.Key)

End Function

Public Function GetIV() As String

Return Convert.ToBase64String(encryptionAlgorithm.IV)

End Function

Public Shared Function GetLegalKey(ByVal KeyString As String) As Byte()

Try

Dim rijaendel As SymmetricAlgorithm = RijndaelManaged.Create()

' Adjust key if necessary, and return a valid key

If rijaendel.LegalKeySizes.Length > 0 Then

' Key sizes in bits

Dim keySize As Integer = KeyString.Length * 8

Dim minSize As Integer = rijaendel.LegalKeySizes(0).MinSize

Dim maxSize As Integer = rijaendel.LegalKeySizes(0).MaxSize

Dim skipSize As Integer = rijaendel.LegalKeySizes(0).SkipSize

If keySize > maxSize Then

' Extract maximum size allowed

KeyString = KeyString.Substring(0, maxSize / 8)

ElseIf keySize < color="blue">Then

' Set valid size

Dim validSize As Integer = If((keySize <= minSize), minSize,(keySize - keySize Mod skipSize) + skipSize)

If keySize < color="blue">Then

' Pad the key with asterisk to make up the size

KeyString = KeyString.PadRight(validSize / 8, "*"c)

End If

Return UTF8Encoding.UTF8.GetBytes(KeyString)

Catch ex As Exception

Return Nothing

End Try

End Function

Public Function EncryptString(ByVal clearText As String) As String

Try

'The purpose of this function is to take plain text and encrypt it using rijaendel algorithm

Dim clearTextBytes As Byte() = Encoding.UTF8.GetBytes(clearText)

Dim encrypted As Byte() = encryptionAlgorithm.CreateEncryptor().TransformFinalBlock(clearTextBytes, 0, clearTextBytes.Length)

Return Convert.ToBase64String(encrypted)

Catch ex As Exception

Return ""

End Try

End Function

Public Function DecryptString(ByVal encryptedEncodedText As String) As String

Try

'The purpose of this function is to take encrypted text and decrypt it using rijaendel algorithm

Dim encryptedBytes As Byte() = Convert.FromBase64String(encryptedEncodedText)

Dim decryptedBytes As Byte() = encryptionAlgorithm.CreateDecryptor().TransformFinalBlock(encryptedBytes, 0, encryptedBytes.Length)

Return Encoding.UTF8.GetString(decryptedBytes)

Catch fe As FormatException

Return ""

Catch e As CryptographicException

Return ""

End Try

End Function

End Class

2009-05-15T13:44:00.000-07:00

I am opening this blog to document answers to .Net Development challenges. I am the co-owner of a small technology consulting company that primarily specializes in developing business applications using the latest Microsoft technologies. You can learn more about my company at http://www.constotech.com

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.NET Encryption Using SymmetricAlgorithm & Rijndael