[openssl-users] Is it mandatory to reverse windows signature while doing verification in OpenSSL?

[Rishabh K Dubey]

Thanks Tom for Quick response.

Regards,
Rishabh

-----Original Message-----
From: openssl-users [mailto:openssl-users-bounces at openssl.org] On Behalf Of Tom Francis
Sent: Wednesday, April 01, 2015 7:17 PM
To: openssl-users at openssl.org
Subject: Re: [openssl-users] Is it mandatory to reverse windows signature while doing verification in OpenSSL?

If you mean you’re using CryptSignHash(), and are reversing the bytes in the resulting signature, then yes, this is normal.  You’ll need to reverse the bytes when verifying the signature with ANY other toolkit/library, including CNG. :)  If it’s not too late, you should store the signature with the bytes reversed, and then reverse the bytes when you want to verify the signature with CryptVerifySignature(), so that nothing else needs to reverse the bytes.  If you later switch from CryptoAPI to CNG, then you’ll be able to remove the byte reversing code, since CNG uses the same byte order as OpenSSL.

CryptoAPI tends to put all large integer data in least significant byte first order (probably because somebody was accustomed to little endian on x86?).  Every other library I’ve used does the opposite, so I strongly recommend any storage be different from what CryptoAPI produces/expects unless your main intent is to work only with CryptoAPI.

TOM


> On Apr 1, 2015, at 2:12 AM, Rishabh K Dubey <rishabh.dubey at igate.com> wrote:
> 
> Dear,
> 
>  
> 
> We have signed data on Win 7 using Crypto APIs and generated signature. We have observed this such reversing of signature bytes is valid operation or not. Thanks in advance.
> 
>  
> 
> Regards,
> 
> Rishabh
> 
> 
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