RSA private key objects

RSA private key objects (object class CKO_PRIVATE_KEY, key type CKK_RSA) hold RSA private keys. The following table defines the RSA private key object attributes, in addition to the common attributes listed in Table 14 , Table 18 , Table 24 , and Table 32 :

Table 34, RSA Private Key Object Attributes

Attribute	Data type	Meaning
CKA_MODULUS^1,4,6	Big integer	Modulus n
CKA_PUBLIC_EXPONENT^4,6	Big integer	Public exponent e
CKA_PRIVATE_EXPONENT^1,4,6,7	Big integer	Private exponent d
CKA_PRIME_1^4,6,7	Big integer	Prime p
CKA_PRIME_2^4,6,7	Big integer	Prime q
CKA_EXPONENT_1^4,6,7	Big integer	Private exponent d modulo p -1
CKA_EXPONENT_2^4,6,7	Big integer	Private exponent d modulo q -1
CKA_COEFFICIENT^4,6,7	Big integer	CRT coefficient q ^-1 mod p

Depending on the token, there may be limits on the length of the key components. See PKCS #1 for more information on RSA keys.

Tokens vary in what they actually store for RSA private keys. Some tokens store all of the above attributes, which can assist in performing rapid RSA computations. Other tokens might store only the CKA_MODULUS and CKA_PRIVATE_EXPONENT values.

Because of this, Cryptoki is flexible in dealing with RSA private key objects. When a token generates an RSA private key, it stores whichever of the fields in Table 34 it keeps track of. Later, if an application asks for the values of the key's various attributes, Cryptoki supplies values only for attributes whose values it can obtain (i.e., if Cryptoki is asked for the value of an attribute it cannot obtain, the request fails). Note that a Cryptoki implementation may or may not be able and/or willing to supply various attributes of RSA private keys which are not actually stored on the token. E.g., if a particular token stores values only for the CKA_PRIVATE_EXPONENT, CKA_PRIME_1, and CKA_PRIME_2 attributes, then Cryptoki is certainly able to report values for all the attributes above (since they can all be computed efficiently from these three values). However, a Cryptoki implementation may or may not actually do this extra computation. The only attributes from Table 34 for which a Cryptoki implementation is required to be able to return values are CKA_MODULUS and CKA_PRIVATE_EXPONENT.

If an RSA private key object is created on a token, and more attributes from Table 34 are supplied to the object creation call than are supported by the token, the extra attributes are likely to be thrown away. If an attempt is made to create an RSA private key object on a token with insufficient attributes for that particular token, then the object creation call fails and returns CKR_TEMPLATE_INCOMPLETE.

Note that when generating an RSA private key, there is no CKA_MODULUS_BITS attribute specified. This is because RSA private keys are only generated as part of an RSA key pair, and the CKA_MODULUS_BITS attribute for the pair is specified in the template for the RSA public key.

CK_OBJECT_CLASS class = CKO_PRIVATE_KEY;
CK_KEY_TYPE keyType = CKK_RSA;
CK_UTF8CHAR label[] = "An RSA private key object";
CK_BYTE subject[] = {...};
CK_BYTE id[] = {123};
CK_BYTE modulus[] = {...};
CK_BYTE publicExponent[] = {...};
CK_BYTE privateExponent[] = {...};
CK_BYTE prime1[] = {...};
CK_BYTE prime2[] = {...};
CK_BYTE exponent1[] = {...};
CK_BYTE exponent2[] = {...};
CK_BYTE coefficient[] = {...};
CK_BBOOL true = TRUE;
CK_ATTRIBUTE template[] = {
{CKA_CLASS, &class, sizeof(class)},
{CKA_KEY_TYPE, &keyType, sizeof(keyType)},
{CKA_TOKEN, &true, sizeof(true)},
{CKA_LABEL, label, sizeof(label)-1},
{CKA_SUBJECT, subject, sizeof(subject)},
{CKA_ID, id, sizeof(id)},
{CKA_SENSITIVE, &true, sizeof(true)},
{CKA_DECRYPT, &true, sizeof(true)},
{CKA_SIGN, &true, sizeof(true)},
{CKA_MODULUS, modulus, sizeof(modulus)},
{CKA_PUBLIC_EXPONENT, publicExponent, sizeof(publicExponent)},
{CKA_PRIVATE_EXPONENT, privateExponent, sizeof(privateExponent)},
{CKA_PRIME_1, prime1, sizeof(prime1)},
{CKA_PRIME_2, prime2, sizeof(prime2)},
{CKA_EXPONENT_1, exponent1, sizeof(exponent1)},
{CKA_EXPONENT_2, exponent2, sizeof(exponent2)},
{CKA_COEFFICIENT, coefficient, sizeof(coefficient)}
};