From aa7b746a1411d291d7b19c5ff989c969a91c8b0b Mon Sep 17 00:00:00 2001
From: xtaci <imap@live.com>
Date: Sun, 22 Dec 2024 19:48:36 +0800
Subject: [PATCH] add a fast PRNG for simple extension of seed, and move
 CreatePRNG to public function

---
 qpp.go      | 21 ++++++++++++++++++---
 qpp_test.go | 19 +++++++++++++++++--
 2 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/qpp.go b/qpp.go
index a6924f8..eedbcf6 100644
--- a/qpp.go
+++ b/qpp.go
@@ -98,8 +98,8 @@ func NewQPP(seed []byte, numPads uint16) *QuantumPermutationPad {
 		reverse(pad, rpad)
 	}
 
-	qpp.encRand = qpp.CreatePRNG(seed) // Create default PRNG for encryption
-	qpp.decRand = qpp.CreatePRNG(seed) // Create default PRNG for decryption
+	qpp.encRand = CreatePRNG(seed) // Create default PRNG for encryption
+	qpp.decRand = CreatePRNG(seed) // Create default PRNG for decryption
 
 	return qpp
 }
@@ -118,7 +118,7 @@ func (qpp *QuantumPermutationPad) Decrypt(data []byte) {
 
 // CreatePRNG creates a deterministic pseudo-random number generator based on the provided seed
 // It uses HMAC and PBKDF2 to derive a random seed for the PRNG
-func (qpp *QuantumPermutationPad) CreatePRNG(seed []byte) *Rand {
+func CreatePRNG(seed []byte) *Rand {
 	mac := hmac.New(sha256.New, seed)
 	mac.Write([]byte(PM_SELECTOR_IDENTIFIER))
 	sum := mac.Sum(nil)
@@ -135,6 +135,21 @@ func (qpp *QuantumPermutationPad) CreatePRNG(seed []byte) *Rand {
 	return rd
 }
 
+// FastPRNG creates a deterministic pseudo-random number generator based on the provided seed
+func FastPRNG(seed []byte) *Rand {
+	sha := sha256.New()
+	sum := sha.Sum(seed)
+
+	// Create and return PRNG
+	rd := &Rand{}
+	rd.xoshiro[0] = binary.LittleEndian.Uint64(sum[0:8])
+	rd.xoshiro[1] = binary.LittleEndian.Uint64(sum[8:16])
+	rd.xoshiro[2] = binary.LittleEndian.Uint64(sum[16:24])
+	rd.xoshiro[3] = binary.LittleEndian.Uint64(sum[24:32])
+	rd.seed64 = xoshiro256ss(&rd.xoshiro)
+	return rd
+}
+
 // EncryptWithPRNG encrypts the data using the Quantum Permutation Pad with a custom PRNG
 // This function shares the same permutation matrices
 func (qpp *QuantumPermutationPad) EncryptWithPRNG(data []byte, rand *Rand) {
diff --git a/qpp_test.go b/qpp_test.go
index 418b163..97b51b3 100644
--- a/qpp_test.go
+++ b/qpp_test.go
@@ -320,11 +320,11 @@ func TestEncryptionMixedPRNG(t *testing.T) {
 	msg := make([]byte, len(original))
 	copy(msg, original)
 
-	rand_enc := qpp.CreatePRNG(seed)
+	rand_enc := CreatePRNG(seed)
 	qpp.EncryptWithPRNG(msg, rand_enc)
 	assert.NotEqual(t, original, msg, "not encrypted")
 
-	rand_dec := qpp.CreatePRNG(seed)
+	rand_dec := CreatePRNG(seed)
 	qpp.DecryptWithPRNG(msg, rand_dec)
 	assert.Equal(t, original, msg, "not equal")
 }
@@ -382,3 +382,18 @@ func BenchmarkRandV2(b *testing.B) {
 		_ = encRand.Uint32()
 	}
 }
+
+func BenchmarkCreatePRNG(b *testing.B) {
+	seed := make([]byte, 32)
+	io.ReadFull(rand.Reader, seed)
+	for i := 0; i < b.N; i++ {
+		_ = CreatePRNG(seed)
+	}
+}
+func BenchmarkFastPRNG(b *testing.B) {
+	seed := make([]byte, 32)
+	io.ReadFull(rand.Reader, seed)
+	for i := 0; i < b.N; i++ {
+		_ = FastPRNG(seed)
+	}
+}