PKCS#11
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| Cryptographic Token Interface Standard |
PKCS#11 |
Cryptographic functions (i.e., any functions falling under one of these categories: encryption functions; decryption functions; message digesting functions; signing and MACing functions; functions for verifying signatures and MACs; dual-purpose cryptographic functions; key management functions; random number generation functions) executing in Cryptoki sessions can periodically surrender control to the application who called them if the session they are executing in had a notification callback function associated with it when it was opened. They do this by calling the session's callback with the arguments (hSession, CKN_SURRENDER, pApplication), where hSession is the session's handle and pApplication was supplied to C_OpenSession when the session was opened. Surrender callbacks should return either the value CKR_OK (to indicate that Cryptoki should continue executing the function) or the value CKR_CANCEL (to indicate that Cryptoki should abort execution of the function). Of course, before returning one of these values, the callback function can perform some computation, if desired.
A typical use of a surrender callback might be to give an application user feedback during a lengthy key pair generation operation. Each time the application receives a callback, it could display an additional "." to the user. It might also examine the keyboard's activity since the last surrender callback, and abort the key pair generation operation (probably by returning the value CKR_CANCEL) if the user hit <ESCAPE>.
A Cryptoki library is not required to make any surrender callbacks.