// Get the public key matching a private key
// TODO: Add support for non-RSA keys, switching on CKA_KEY_TYPE
func getPublicKey(module *pkcs11.Ctx, session pkcs11.SessionHandle, privateKeyHandle pkcs11.ObjectHandle) (rsa.PublicKey, error) {
var noKey rsa.PublicKey
template := []*pkcs11.Attribute{
pkcs11.NewAttribute(pkcs11.CKA_MODULUS, nil),
pkcs11.NewAttribute(pkcs11.CKA_PUBLIC_EXPONENT, nil),
}
attr, err := module.GetAttributeValue(session, privateKeyHandle, template)
if err != nil {
return noKey, err
}
n := big.NewInt(0)
e := int(0)
gotModulus, gotExponent := false, false
for _, a := range attr {
if a.Type == pkcs11.CKA_MODULUS {
n.SetBytes(a.Value)
gotModulus = true
} else if a.Type == pkcs11.CKA_PUBLIC_EXPONENT {
bigE := big.NewInt(0)
bigE.SetBytes(a.Value)
e = int(bigE.Int64())
gotExponent = true
}
}
if !gotModulus || !gotExponent {
return noKey, errors.New("public key missing either modulus or exponent")
}
return rsa.PublicKey{
N: n,
E: e,
}, nil
}
func (ps *Key) getPrivateKey(module *pkcs11.Ctx, session pkcs11.SessionHandle, label string) (pkcs11.ObjectHandle, error) {
var noHandle pkcs11.ObjectHandle
template := []*pkcs11.Attribute{
pkcs11.NewAttribute(pkcs11.CKA_CLASS, pkcs11.CKO_PRIVATE_KEY),
pkcs11.NewAttribute(pkcs11.CKA_LABEL, label),
}
if err := module.FindObjectsInit(session, template); err != nil {
return noHandle, err
}
objs, _, err := module.FindObjects(session, 2)
if err != nil {
return noHandle, err
}
if err = module.FindObjectsFinal(session); err != nil {
return noHandle, err
}
if len(objs) == 0 {
return noHandle, fmt.Errorf("private key not found")
}
privateKeyHandle := objs[0]
// Check whether the key has the CKA_ALWAYS_AUTHENTICATE attribute.
// If so, fail: we don't want to have to re-authenticate for each sign
// operation.
attributes, err := module.GetAttributeValue(session, privateKeyHandle, []*pkcs11.Attribute{
pkcs11.NewAttribute(pkcs11.CKA_ALWAYS_AUTHENTICATE, false),
})
// The PKCS#11 spec states that C_GetAttributeValue may return
// CKR_ATTRIBUTE_TYPE_INVALID if an object simply does not posses a given
// attribute. We don't consider that an error: the absence of the
// CKR_ATTRIBUTE_TYPE_INVALID property is just fine.
if err != nil && err == pkcs11.Error(pkcs11.CKR_ATTRIBUTE_TYPE_INVALID) {
return privateKeyHandle, nil
} else if err != nil {
return noHandle, err
}
for _, attribute := range attributes {
if len(attribute.Value) > 0 && attribute.Value[0] == 1 {
ps.alwaysAuthenticate = true
}
}
return privateKeyHandle, nil
}
