Cryptographic Token Interface Standard

PKCS#11

RC5-CBC

RC5-CBC, denoted CKM_RC5_CBC, is a mechanism for single- and multiple-part encryption and decryption; key wrapping; and key unwrapping, based on RSA Data Security's block cipher RC5 and cipher-block chaining mode as defined in FIPS PUB 81.

It has a parameter, a CK_RC5_CBC_PARAMS structure, which specifies the wordsize and number of rounds of encryption to use, as well as the initialization vector for cipher block chaining mode.

This mechanism can wrap and unwrap any secret key. Of course, a particular token may not be able to wrap/unwrap every secret key that it supports. For wrapping, the mechanism encrypts the value of the CKA_VALUE attribute of the key that is wrapped, padded on the trailing end with up to seven null bytes so that the resulting length is a multiple of eight. The output data is the same length as the padded input data. It does not wrap the key type, key length, or any other information about the key; the application must convey these separately.

For unwrapping, the mechanism decrypts the wrapped key, and truncates the result according to the CKA_KEY_TYPE attribute of the template and, if it has one, and the key type supports it, the CKA_VALUE_LEN attribute of the template. The mechanism contributes the result as the CKA_VALUE attribute of the new key; other attributes required by the key type must be specified in the template.

Constraints on key types and the length of data are summarized in the following table: 




 Table 76, RC5-CBC: Key And Data Length   
Function Key type 

Input length

 

Output length

 

Comments

   


C_Encrypt RC5 

multiple of blocksize

 

same as input length

 

no final part

   


C_Decrypt RC5 

multiple of blocksize

 

same as input length

 

no final part

   


C_WrapKey RC5 

any

 

input length rounded up to multiple of blocksize

 		    


C_UnwrapKey RC5 

multiple of blocksize

 

determined by type of key being unwrapped or CKA_VALUE_LEN

 		   

 



 
 



RSA Security Inc. Public-Key Cryptography Standards - 
PKCS#11 - v210