PKCS #3 Diffie-Hellman key derivation

The PKCS #3 Diffie-Hellman key derivation mechanism, denoted CKM_DH_PKCS_DERIVE, is a mechanism for key derivation based on Diffie-Hellman key agreement, as defined in PKCS #3. This is what PKCS #3 calls "phase II".

It has a parameter, which is the public value of the other party in the key agreement protocol, represented as a Cryptoki "Big integer" (i.e., a sequence of bytes, most-significant byte first).

This mechanism derives a secret key from a Diffie-Hellman private key and the public value of the other party. It computes a Diffie-Hellman secret value from the public value and private key according to PKCS #3, 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 truncation removes bytes from the leading end of the secret value.) 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.

The derived key inherits the values of the CKA_SENSITIVE, CKA_ALWAYS_SENSITIVE, CKA_EXTRACTABLE, and CKA_NEVER_EXTRACTABLE attributes from the base key. The values of the CKA_SENSITIVE and CKA_EXTRACTABLE attributes may be overridden in the template for the derived key, however. Of course, if the base key has the CKA_ALWAYS_SENSITIVE attribute set to TRUE, then the template may not specify that the derived key should have the CKA_SENSITIVE attribute set to FALSE; similarly, if the base key has the CKA_NEVER_EXTRACTABLE attribute set to TRUE, then the template may not specify that the derived key should have the CKA_EXTRACTABLE attribute set to TRUE.

For this mechanism, the ulMinKeySize and ulMaxKeySize fields of the CK_MECHANISM_INFO structure specify the supported range of Diffie-Hellman prime sizes, in bits.

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