signature/policy_config.go
func (kt sbKeyType) IsValid() bool {
	switch kt {
	case SBKeyTypeGPGKeys, SBKeyTypeSignedByGPGKeys,
		SBKeyTypeX509Certificates, SBKeyTypeSignedByX509CAs:
		return true
	default:
		return false
	}
}
func (kt sbKeyType) IsValid() bool {
	switch kt {
	case SBKeyTypeGPGKeys, SBKeyTypeSignedByGPGKeys,
		SBKeyTypeX509Certificates, SBKeyTypeSignedByX509CAs:
		return true
	default:
		return false
	}
}
// IsValid returns true iff kt is a recognized value