// Copyright 2024 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package mlkem

import (
	"bytes"
	"crypto/internal/fips140"
	_ "crypto/internal/fips140/check"
	"crypto/internal/fips140/sha256"
	"errors"
	"sync"
)

var fipsSelfTest = sync.OnceFunc(func() {
	fips140.CAST("ML-KEM-768", fips140CAST)
})

// fips140CAST covers both the successful and the implicit rejection paths, as
// required by IG 10.3.A, Resolution 14, and as tested by TestCASTRejectionPath.
// It tests only one parameter set as allowed by Note22. It compares dk and not
// ek, because ek is part of dk, as allowed by the same Resolution. It compares
// dk with an expected hash to avoid embedding several kilobytes of test vectors
// in every binary, as allowed by GeneralNote7.
func fips140CAST() error {
	var d = &[32]byte{
		0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
		0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x10,
		0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18,
		0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20,
	}
	var z = &[32]byte{
		0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28,
		0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30,
		0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38,
		0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f, 0x40,
	}
	var dkHash = []byte{
		0xa1, 0x32, 0x4a, 0x71, 0xf5, 0x7e, 0x26, 0x85,
		0x37, 0x7e, 0x4f, 0x7d, 0xe2, 0xd1, 0xf0, 0x58,
		0x53, 0x8e, 0x08, 0x7e, 0xe3, 0x9b, 0x48, 0x2b,
		0x3d, 0xbf, 0x96, 0xf9, 0xf7, 0x69, 0xc7, 0x85,
	}
	var m = &[32]byte{
		0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48,
		0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50,
		0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58,
		0x59, 0x5a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f, 0x60,
	}
	var K = []byte{
		0x55, 0x01, 0xfc, 0x52, 0x3b, 0x74, 0x5f, 0x41,
		0x76, 0x2a, 0x18, 0x8d, 0xe4, 0x4a, 0x59, 0xb9,
		0x20, 0xf4, 0x30, 0x14, 0x62, 0x04, 0xee, 0x4e,
		0x79, 0x37, 0x32, 0x39, 0x6d, 0xf7, 0xaa, 0x48,
	}
	var Kr = []byte{
		0x01, 0xa1, 0x03, 0x3a, 0x2e, 0x68, 0x33, 0x80,
		0x7f, 0xd3, 0x91, 0x80, 0xbe, 0x3b, 0x4f, 0x0a,
		0x1f, 0x6f, 0x50, 0x51, 0x67, 0x56, 0x9d, 0x0e,
		0x5e, 0x5e, 0x1f, 0xdb, 0x52, 0xa9, 0x10, 0xec,
	}
	dk := &DecapsulationKey768{}
	kemKeyGen(dk, d, z)
	ek := dk.EncapsulationKey()
	H := sha256.New()
	H.Write(TestingOnlyExpandedBytes768(dk))
	if !bytes.Equal(H.Sum(nil), dkHash) {
		return errors.New("unexpected private key hash")
	}
	var cc [CiphertextSize768]byte
	Kd := kemDecaps(dk, &cc)
	if !bytes.Equal(Kd, Kr) {
		return errors.New("unexpected rejection result")
	}
	Ke, _ := kemEncaps(&cc, ek, m)
	Kd = kemDecaps(dk, &cc)
	if !bytes.Equal(Ke, K) || !bytes.Equal(Kd, K) {
		return errors.New("unexpected result")
	}
	return nil
}