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Understanding of SignedCms.CheckSignature(True)

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An understanding of SignedCms.CheckSignature(True) based on the code stated below.

' Create a ContentInfo object from the inner content obtained

' independently from encodedMessage.

Dim contentInfo As New ContentInfo(innerContent)

 

' Create a new, detached SignedCms message.

Dim signedCms As New SignedCms(contentInfo, True)

 

' encodedMessage is the encoded message received from

' the sender.

signedCms.Decode(encodedMessage)

 

' Verify the signature without validating the

' certificate.

signedCms.CheckSignature(True)

 

  • We have the innerContent (unsigned), which is message.
  • We have the detached signature, which is the encrypted hash of message.

 

 

Now the code.

  • Dim signedCms As New SignedCms(contentInfo, True) // This detaches the signature and the message, and signature here is the encrypted hash of message.
  • signedCms.Decode(message) // This decodes the encrypted hash of message to give the hash of the message.
  • signedCms.CheckSignature(True) // This does the Compare as shown above by computing the hash of Message and then verifying the hash we got above.

 

References:

https://msdn.microsoft.com/en-us/library/system.security.cryptography.pkcs.signedcms.decode(VS.85).aspx

https://msdn.microsoft.com/en-us/library/system.security.cryptography.pkcs.signedcms(VS.85).aspx