Re: Crypto API using RC2 instead of RC4?

From: Valery Pryamikov (valery_at_harper.no)
Date: 11/22/05 

Date: Tue, 22 Nov 2005 22:35:00 +0100

Hi,
RC2 is block cipher, while as RC4 is stream cipher (or random bytes
generator that you XOR with plain text to get cipher). Block cipher could
only work on complete blocks. Stream ciphers could work with any amount of
bytes (or even bits). Block cipher requires padding, stream cipher doesn't.

and btw. why are you trying to use old and unhealthy RC2 when you can use
AES instead?

-Valery.
http://www.harper.no/valery

"Matt" <mtaylor@gladstonemrm.com> wrote in message
news:1132682536.753106.270920@g49g2000cwa.googlegroups.com...
> Hello,
>
> The code below works fine for encrypting and decrypting but I need to
> change it to use RC2 instead of RC4.
> This is because the .NET application that is going to do the decrypting
> uses RC2.
>
> I thought it would be a simple matter of changing the ENCRYPT_ALGORITHM
> constant to CALG_RC2, but doing this causes the decrypt to fail with
> complaints about the number of bytes.
>
> This code is very much a work in progress and is based on some that I
> found here:
> http://groups.google.co.uk/group/microsoft.public.vb.winapi/browse_thread/thread/ef6301b4cd280e0b/9358960af9b30916
>
> I hope someone can help.
>
> Thanks in advance.
>
> Matt
>
> ** Start Code **
>
> Public sPassword As String
> Public sInputBuffer As String
> Public sOutputBuffer As String
>
> 'constants for Cryptography API functions
> Private Const CRYPT_NEWKEYSET = &H8
> Private Const MS_DEF_PROV = "Microsoft Base Cryptographic Provider
> v1.0"
> Private Const PROV_RSA_FULL = 1
> Private Const ALG_CLASS_DATA_ENCRYPT = 24576
> Private Const ALG_CLASS_HASH = 32768
>
> Private Const ALG_TYPE_ANY = 0
> Private Const ALG_TYPE_BLOCK = 1536
> Private Const ALG_TYPE_STREAM = 2048
> Private Const ALG_SID_RC2 = 2
> Private Const ALG_SID_RC4 = 1
> Private Const ALG_SID_MD5 = 3
> Private Const ALG_SID_SHA1 = 4
>
> Private Const CALG_MD5 = ((ALG_CLASS_HASH Or ALG_TYPE_ANY) Or
> ALG_SID_MD5)
> Private Const CALG_RC2 = ((ALG_CLASS_DATA_ENCRYPT Or ALG_TYPE_BLOCK) Or
> ALG_SID_RC2)
> Private Const CALG_RC4 = ((ALG_CLASS_DATA_ENCRYPT Or ALG_TYPE_STREAM)
> Or ALG_SID_RC4)
> Private Const CALG_SHA1 = ALG_CLASS_HASH Or ALG_TYPE_ANY Or
> ALG_SID_SHA1
>
> Private Const ENCRYPT_ALGORITHM = CALG_RC4
>
> Public Sub CryptoEncrypt()
>
> Dim lHHash As Long
> Dim lHkey As Long
> Dim lResult As Long
> Dim lHExchgKey As Long
> Dim lHCryptprov As Long
>
> Dim sContainer As String
> Dim lCryptLength As Long
> Dim lCryptBufLen As Long
> Dim sCryptBuffer As String
>
> On Error GoTo EncryptError
>
> 'Get handle to the default CSP
> sProvider = MS_DEF_PROV & vbNullChar
> If Not CBool(CryptAcquireContext(lHCryptprov, 0&, sProvider,
> PROV_RSA_FULL, 0)) Then
> 'If there is no default key container then create one using
> Flags field
> If GetLastError = 0 Then
> If Not CBool(CryptAcquireContext(lHCryptprov, 0&, sProvider,
> PROV_RSA_FULL, CRYPT_NEWKEYSET)) Then
> MsgBox ("Error " & CStr(GetLastError) & " during
> CryptAcquireContext! ")
> GoTo Finished
> End If
> End If
> End If
>
> 'Create a hash object
> If Not CBool(CryptCreateHash(lHCryptprov, CALG_SHA1, 0, 0, lHHash))
> Then
> MsgBox ("Error " & CStr(GetLastError) & " during
> CryptCreateHash!")
> GoTo Finished
> End If
>
> 'Hash in the password text
> If Not CBool(CryptHashData(lHHash, sPassword, Len(sPassword), 0))
> Then
> MsgBox ("Error " & CStr(GetLastError) & " during
> CryptHashData!")
> GoTo Finished
> End If
>
> 'Create a session key from the hash object.
> If Not CBool(CryptDeriveKey(lHCryptprov, ENCRYPT_ALGORITHM, lHHash,
> 0, lHkey)) Then
> MsgBox ("Error " & CStr(GetLastError) & " during
> CryptDeriveKey!")
> GoTo Finished
> End If
>
> 'Destroy the hash object.
> CryptDestroyHash (lHHash)
> lHHash = 0
>
> 'Create a buffer for the CryptEncrypt function
> lCryptLength = Len(sInputBuffer)
> lCryptBufLen = lCryptLength * 2
> sCryptBuffer = String(lCryptBufLen, vbNullChar)
> LSet sCryptBuffer = sInputBuffer
>
> 'Encrypt the text data
> If Not CBool(CryptEncrypt(lHkey, 0, 1, 0, sCryptBuffer,
> lCryptLength, lCryptBufLen)) Then
> MsgBox ("bytes required:" & CStr(lCryptLength))
> MsgBox ("Error " & CStr(GetLastError) & " during CryptEncrypt!")
> End If
>
> sOutputBuffer = Mid$(sCryptBuffer, 1, lCryptLength)
>
> Finished:
>
> 'Destroy session key.
> If (lHkey) Then lResult = CryptDestroyKey(lHkey)
>
> 'Destroy key exchange key handle
> If lHExchgKey Then CryptDestroyKey (lHExchgKey)
>
> 'Destroy hash object
> If lHHash Then CryptDestroyHash (lHHash)
>
> 'Release Context provider handle
> If lHCryptprov Then lResult = CryptReleaseContext(lHCryptprov, 0)
>
> Exit Sub
>
> EncryptError:
>
> MsgBox ("Encrypt Error: " & Error$)
>
> GoTo Finished
>
> End Sub
>
> Public Sub CryptoDecrypt()
> Dim lHExchgKey As Long
> Dim lHCryptprov As Long
> Dim lHHash As Long
> Dim lHkey As Long
> Dim lResult As Long
>
> Dim sProvider As String
>
> Dim sCryptBuffer As String
> Dim lCryptBufLen As Long
> Dim lCryptPoint As Long
>
> Dim lPasswordPoint As Long
> Dim lPasswordCount As Long
>
> On Error GoTo DecryptError
>
> 'Clear the Output buffer
> sOutputBuffer = ""
>
> 'Get handle to the default CSP.
> sProvider = vbNullChar
> sProvider = MS_DEF_PROV & vbNullChar
> If Not CBool(CryptAcquireContext(lHCryptprov, 0&, sProvider,
> PROV_RSA_FULL, 0)) Then
> MsgBox ("Error " & CStr(GetLastError) & " during
> CryptAcquireContext!")
> GoTo Finished
> End If
>
> 'Create a hash object
> If Not CBool(CryptCreateHash(lHCryptprov, CALG_SHA1, 0, 0, lHHash))
> Then
> MsgBox ("Error " & CStr(GetLastError) & " during
> CryptCreateHash!")
> GoTo Finished
> End If
>
> 'Hash in the password text
> If Not CBool(CryptHashData(lHHash, sPassword, Len(sPassword), 0))
> Then
> MsgBox ("Error " & CStr(GetLastError) & " during
> CryptHashData!")
> GoTo Finished
> End If
>
> 'Create a session key from the hash object
> If Not CBool(CryptDeriveKey(lHCryptprov, ENCRYPT_ALGORITHM, lHHash,
> 0, lHkey)) Then
> MsgBox ("Error " & CStr(GetLastError) & " during
> CryptDeriveKey!")
> GoTo Finished
> End If
>
> 'Destroy the hash object.
> CryptDestroyHash (lHHash)
> lHHash = 0
>
> 'Prepare sCryptBuffer for CryptDecrypt
> lCryptBufLen = Len(sInputBuffer) * 2
> sCryptBuffer = String(lCryptBufLen, vbNullChar)
> LSet sCryptBuffer = sInputBuffer
>
> 'Decrypt data
> If Not CBool(CryptDecrypt(lHkey, 0, 1, 0, sCryptBuffer,
> lCryptBufLen)) Then
> MsgBox ("bytes required:" & CStr(lCryptBufLen))
> MsgBox ("Error " & CStr(GetLastError) & " during CryptDecrypt!")
> GoTo Finished
> End If
>
> 'Setup output buffer with just decrypted data
> sOutputBuffer = Mid$(sCryptBuffer, 1, lCryptBufLen / 2)
>
> Finished:
>
> 'Destroy session key
> If (lHkey) Then lResult = CryptDestroyKey(lHkey)
>
> 'Destroy key exchange key handle
> If lHExchgKey Then CryptDestroyKey (lHExchgKey)
>
> 'Destroy hash object
> If lHHash Then CryptDestroyHash (lHHash)
>
> 'Release Context provider handle
> If lHCryptprov Then lResult = CryptReleaseContext(lHCryptprov, 0)
>
> Exit Sub
>
> DecryptError:
> MsgBox ("Decrypt Error: " & Error$)
> GoTo Finished
>
> End Sub
>
> ** End Code **
>

Relevant Pages

  • Re: how these 2 functions may differ?
    ... The original encryption and base64 encoding is done from a Windows Script Host vbscript. ... cipher += Microsoft.VisualBasic.Strings.Chr; ... Dim sbox ...
    (microsoft.public.dotnet.languages.csharp)
  • Re: Byte Array Speed
    ... Private Sub Bcipher() ... Dim MaskAs Byte ... Dim Eflg As String * 2 ... >> Years ago I wrote a simple Cipher program in DOS Assembler. ...
    (microsoft.public.vb.general.discussion)
  • Re: Bad Data error in DES encryption
    ... Cipher text is binary randomly looking data, ... > I'm doing a symmetric encryption using DES provider. ... > Dim encAlg As New DESCryptoServiceProvider ...
    (microsoft.public.dotnet.security)
  • Crypto API using RC2 instead of RC4?
    ... This is because the .NET application that is going to do the decrypting ... Private Const MS_DEF_PROV = "Microsoft Base Cryptographic Provider ... Dim lHHash As Long ... 'Create a session key from the hash object. ...
    (microsoft.public.platformsdk.security)