func I64(key []byte, data []byte) ([]byte, []byte) {
	mac := hmac.New(sha512.New, key)
	mac.Write(data)
	I := mac.Sum(nil)
	return I[:32], I[32:]
}
func I64(key []byte, data []byte) ([]byte, []byte) {
	mac := hmac.New(sha512.New, key)
	mac.Write(data)
	I := mac.Sum(nil)
	return I[:32], I[32:]
}
func I64 ( key [ ] byte , data [ ] byte ) ( [ ] byte , [ ] byte ) { mac := hmac . New ( sha512 . New , key ) mac . Write ( data ) I := mac . Sum ( nil ) return I [ : 32 ] , I [ 32 : ] }
// I64 returns the two halfs of the SHA512 HMAC of key and data.
I64 returns the two halfs of the SHA512 HMAC of key and data .