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core/primes.go

@@ -0,0 +1,42 @@
+//
+// Copyright Coinbase, Inc. All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+package core
+
+import (
+	"crypto/rand"
+	"fmt"
+	"math"
+	"math/big"
+)
+
+// GenerateSafePrime creates a prime number `p`
+// where (`p`-1)/2 is also prime with at least `bits`
+func GenerateSafePrime(bits uint) (*big.Int, error) {
+	if bits < 3 {
+		return nil, fmt.Errorf("safe prime size must be at least 3-bits")
+	}
+
+	var p *big.Int
+	var err error
+	checks := int(math.Max(float64(bits)/16, 8))
+	for {
+		// rand.Prime throws an error if bits < 2
+		// -1 so the Sophie-Germain prime is 1023 bits
+		// and the Safe prime is 1024
+		p, err = rand.Prime(rand.Reader, int(bits)-1)
+		if err != nil {
+			return nil, err
+		}
+		p.Add(p.Lsh(p, 1), One)
+
+		if p.ProbablyPrime(checks) {
+			break
+		}
+	}
+
+	return p, nil
+}