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//go:build gofuzz
// +build gofuzz
// How to run the fuzzer:
//
// $ go get -u github.com/dvyukov/go-fuzz/go-fuzz
// $ go get -u github.com/dvyukov/go-fuzz/go-fuzz-build
// $ go-fuzz-build -libfuzzer -func FuzzReduction -o lib.a
// $ clang -fsanitize=fuzzer lib.a -o fu.exe
// $ ./fu.exe
package fp448
import (
"encoding/binary"
"fmt"
"math/big"
"github.com/cloudflare/circl/internal/conv"
)
// FuzzReduction is a fuzzer target for red64 function, which reduces t
// (112 bits) to a number t' (56 bits) congruent modulo p448.
func FuzzReduction(data []byte) int {
if len(data) != 2*Size {
return -1
}
var got, want Elt
var lo, hi [7]uint64
a := data[:Size]
b := data[Size:]
lo[0] = binary.LittleEndian.Uint64(a[0*8 : 1*8])
lo[1] = binary.LittleEndian.Uint64(a[1*8 : 2*8])
lo[2] = binary.LittleEndian.Uint64(a[2*8 : 3*8])
lo[3] = binary.LittleEndian.Uint64(a[3*8 : 4*8])
lo[4] = binary.LittleEndian.Uint64(a[4*8 : 5*8])
lo[5] = binary.LittleEndian.Uint64(a[5*8 : 6*8])
lo[6] = binary.LittleEndian.Uint64(a[6*8 : 7*8])
hi[0] = binary.LittleEndian.Uint64(b[0*8 : 1*8])
hi[1] = binary.LittleEndian.Uint64(b[1*8 : 2*8])
hi[2] = binary.LittleEndian.Uint64(b[2*8 : 3*8])
hi[3] = binary.LittleEndian.Uint64(b[3*8 : 4*8])
hi[4] = binary.LittleEndian.Uint64(b[4*8 : 5*8])
hi[5] = binary.LittleEndian.Uint64(b[5*8 : 6*8])
hi[6] = binary.LittleEndian.Uint64(b[6*8 : 7*8])
red64(&got, &lo, &hi)
t := conv.BytesLe2BigInt(data[:2*Size])
two448 := big.NewInt(1)
two448.Lsh(two448, 448) // 2^448
mask448 := big.NewInt(1)
mask448.Sub(two448, mask448) // 2^448-1
two224plus1 := big.NewInt(1)
two224plus1.Lsh(two224plus1, 224)
two224plus1.Add(two224plus1, big.NewInt(1)) // 2^224+1
var loBig, hiBig big.Int
for t.Cmp(two448) >= 0 {
loBig.And(t, mask448)
hiBig.Rsh(t, 448)
t.Mul(&hiBig, two224plus1)
t.Add(t, &loBig)
}
conv.BigInt2BytesLe(want[:], t)
if got != want {
fmt.Printf("in: %v\n", conv.BytesLe2BigInt(data[:2*Size]))
fmt.Printf("got: %v\n", got)
fmt.Printf("want: %v\n", want)
panic("error found")
}
return 1
}
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