RC4 CryptoAPI Encryption Password Verification

re: RC4 CryptoAPI Encryption Password Verification

FSS2012 — Tue, 20 Nov 2012 21:46:33 GMT

I am using VB Express 2010 .NET 4.0 client profile and trying to build an office password verifier routine. Using your test data above I have successfully gotten your output for Steps 1, 2, and 4. I am stumped on Step 3 as I cannot get the expected output from the RC4 operation on the EncryptedVerifierHash utilizing the same derived encryption key. Here is the output I am getting from each of the steps:

Step 1a (H ought): 99-1A-E8-18-8C-B3-9B-43-AC-AA-BA-8B-19-2C-6D-30-44-97-38-53

Step 1b (H Final): D7-BE-C9-31-88-E3-39-D7-7E-1B-99-1E-DF-47-C9-8C-8D-6A-99-40

Step 1c (Derived Key): D7-BE-C9-31-88-00-00-00-00-00-00-00-00-00-00-00

Step 2 (Decrypted Verifier): 44-65-87-98-44-00-00-10-11-41-65-AA-A8-BA-DC-ED

**Step 3 (Decrypted Verifier Hash): 59-48-2F-90-B0-F0-20-8E-ED-60-10-DD-5C-7A-F7-3E-D7-3B-1D-B2

'Step 4 (Hashed Decrypted Verifier): 97-17-92-03-C1-89-6A-33-C2-C1-E8-02-A6-76-6F-8B-24-E4-B0-7C

For Step 3: I have set the array below for the Encrypted Verifier Hash

Dim testencryptedVerifierHashValue As Byte() = {&HB6, &H35, &H94, &H44, &H7F, &HAE, &H7D, &H49, &H45, &HD2, &HDA, &HFD, &H11, &H3F, &HD8, &HC9, &HF6, &H19, &H1B, &HF5}

And I pass it, along with the Derived Key (Step 1c) to the RC4 routine.

Dim testDecryptedVerifierHash() As Byte = RC4EnDeCrypt(testencryptedVerifierHashValue, testDerivedKey)

I would expect the output of this to be 97-17... but I get 59-48... What am I missing?

Thank you for your insight and assistance.

re: RC4 CryptoAPI Encryption Password Verification

Norman — Mon, 23 Jan 2012 16:21:11 GMT

Quick question how do I get to EcrptionVerifier.Salt if the password I have needs to use the Salt to decrypt the CryptSession10Container.data in which the Salt is located? Isn't this chicken and egg scenario? Per msdn.microsoft.com/.../dd951371(v=office.12).aspx : The data field of this CryptSession10Container record MUST be encrypted as specified in [MS-OFFCRYPTO] section 2.3.5.1.

Please help. I am trying to figure out how to decrypt a Powerpoint Binary File with given password.

Thank you in advance.

RC4 CryptoAPI Encryption Password Verification | ASP NET Hosting

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