fuzzer.go raw

   1  //go:build gofuzz
   2  // +build gofuzz
   3  
   4  // How to run the fuzzer:
   5  //
   6  //	$ go get -u github.com/dvyukov/go-fuzz/go-fuzz
   7  //	$ go get -u github.com/dvyukov/go-fuzz/go-fuzz-build
   8  //	$ go-fuzz-build -libfuzzer -func FuzzReduction -o lib.a
   9  //	$ clang -fsanitize=fuzzer lib.a -o fu.exe
  10  //	$ ./fu.exe
  11  package fp448
  12  
  13  import (
  14  	"encoding/binary"
  15  	"fmt"
  16  	"math/big"
  17  
  18  	"github.com/cloudflare/circl/internal/conv"
  19  )
  20  
  21  // FuzzReduction is a fuzzer target for red64 function, which reduces t
  22  // (112 bits) to a number t' (56 bits) congruent modulo p448.
  23  func FuzzReduction(data []byte) int {
  24  	if len(data) != 2*Size {
  25  		return -1
  26  	}
  27  	var got, want Elt
  28  	var lo, hi [7]uint64
  29  	a := data[:Size]
  30  	b := data[Size:]
  31  	lo[0] = binary.LittleEndian.Uint64(a[0*8 : 1*8])
  32  	lo[1] = binary.LittleEndian.Uint64(a[1*8 : 2*8])
  33  	lo[2] = binary.LittleEndian.Uint64(a[2*8 : 3*8])
  34  	lo[3] = binary.LittleEndian.Uint64(a[3*8 : 4*8])
  35  	lo[4] = binary.LittleEndian.Uint64(a[4*8 : 5*8])
  36  	lo[5] = binary.LittleEndian.Uint64(a[5*8 : 6*8])
  37  	lo[6] = binary.LittleEndian.Uint64(a[6*8 : 7*8])
  38  
  39  	hi[0] = binary.LittleEndian.Uint64(b[0*8 : 1*8])
  40  	hi[1] = binary.LittleEndian.Uint64(b[1*8 : 2*8])
  41  	hi[2] = binary.LittleEndian.Uint64(b[2*8 : 3*8])
  42  	hi[3] = binary.LittleEndian.Uint64(b[3*8 : 4*8])
  43  	hi[4] = binary.LittleEndian.Uint64(b[4*8 : 5*8])
  44  	hi[5] = binary.LittleEndian.Uint64(b[5*8 : 6*8])
  45  	hi[6] = binary.LittleEndian.Uint64(b[6*8 : 7*8])
  46  
  47  	red64(&got, &lo, &hi)
  48  
  49  	t := conv.BytesLe2BigInt(data[:2*Size])
  50  
  51  	two448 := big.NewInt(1)
  52  	two448.Lsh(two448, 448) // 2^448
  53  	mask448 := big.NewInt(1)
  54  	mask448.Sub(two448, mask448) // 2^448-1
  55  	two224plus1 := big.NewInt(1)
  56  	two224plus1.Lsh(two224plus1, 224)
  57  	two224plus1.Add(two224plus1, big.NewInt(1)) // 2^224+1
  58  
  59  	var loBig, hiBig big.Int
  60  	for t.Cmp(two448) >= 0 {
  61  		loBig.And(t, mask448)
  62  		hiBig.Rsh(t, 448)
  63  		t.Mul(&hiBig, two224plus1)
  64  		t.Add(t, &loBig)
  65  	}
  66  	conv.BigInt2BytesLe(want[:], t)
  67  
  68  	if got != want {
  69  		fmt.Printf("in:   %v\n", conv.BytesLe2BigInt(data[:2*Size]))
  70  		fmt.Printf("got:  %v\n", got)
  71  		fmt.Printf("want: %v\n", want)
  72  		panic("error found")
  73  	}
  74  	return 1
  75  }
  76