Dear Sven, First of all thank you for your prompt reply. I will try and include the information you have requested. The SHA256 implementation comes from here http://smalltalkhub.com/#!/~Cryptography/Cryptography and I loaded only the latest version of Cryptography into a fresh pharo 2.0 image, and nothing else. I need this hmacsha256 encryption for a rest implementation I am trying out, for which I have a VB implementation and I get the correct values for both sets of data. It seems that the SHA256 (encodedSignature) hex value is correct on both occasions and the base64 encodedForHTTP value for the apiKey := '123456789' is also correct, but for the case where apiKey := 'veQC+IBLq5qMO8oGcQupjg==' I get the base64 encodedForHTTP value of 'AcTXF%2BlDa2kRYVm0k5jY6pGGTMXD7NsQS6tLBXRp3Xs%3D' where I should get '%2B%2FYhVkcaEIHBeUESOsJYD1nKyJXVGyFX%2FlxR616aUK4%3D'. The two sets of testing code are: 1) Produces correct result. apiKey := '123456789'. unsignedSignature := 'pharmacistprescriptionsget000001'. encodedSignature := (SHA256 new) hmac key: apiKey asByteArray; digestMessage: unsignedSignature asByteArray. encodedSignature base64Encoded encodeForHTTP. 2) apiKey := 'veQC+IBLq5qMO8oGcQupjg=='. userName := 'testpharm'. barCode :='1403122014500'. unsignedSignature := userName,'prescriptionsgetexecuted',barCode. encodedSignature := (SHA256 new) hmac key: apiKey asByteArray; digestMessage: unsignedSignature asByteArray. encodedSignature base64Encoded encodeForHTTP. Is the above enough? Regards, Spilios Now I understand why I see the long emails/replies! -- View this message in context: http://forum.world.st/Base64-or-HMAC-problem-tp4756788p4756814.html Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com.