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Subject: stackoverflow question: CKA_VALUE_LEN attribute and Unwrap key


All,

 

maybe you’ve seen this already, if not have a look: https://crypto.stackexchange.com/questions/86011/pkcs11-cka-value-len-attribute-and-unwrap-key

 

The inquirer seems to be right. If an AES key is wrapped with a mechanisms employing zero-padding (which is not only AES-ECB or CBC but also CKM_RSA_X_509 or BLOWFISH-CBC) the unwrapped key might contain zeros. The question is how an implementation should proceed now: try to figure out if the AES key has 128, 192 or 256 bits by removing as many zeros as possible (from the end where padding took place during wrap) and rounding up to 128, 192, 256 bits again? Or requiring CKA_VALUE_LEN?

 

Requiring CKA_VALUE_LEN would violate footnote 6 in table 70. Maybe this footnote is just wrong here? There is no footnote with the meaning “must only be given if padding does not encode original length information”…

 

Regards,

Daniel

 




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