func TestRecoverEncodings(t *testing.T) {
constr, key := testConstruction()
fastConstr := fastTestConstruction()
baseConstr := saes.Construction{key}
roundKeys := baseConstr.StretchedKey()
outAff := getOutputAffineEncoding(constr, fastConstr, 1, 0)
// Manually recover the output encoding.
Q, Ps := RecoverEncodings(fastConstr, 1, 0)
if fmt.Sprintf("%x %v", outAff.Linear, outAff.Constant) != fmt.Sprintf("%x %v", Q.Linear, Q.Constant) {
t.Fatalf("RecoverEncodings recovered the wrong output encoding!")
}
// Verify that all Ps composed with their corresponding output encoding equals XOR by a key byte.
id := matrix.GenerateIdentity(8)
for pos, P := range Ps {
outAff := getOutputAffineEncoding(constr, fastConstr, 0, unshiftRows(pos))
A, b := DecomposeAffineEncoding(encoding.ComposedBytes{outAff, P})
if fmt.Sprintf("%x", id) != fmt.Sprintf("%x", A) {
t.Fatalf("Linear part of encoding was not identity!")
}
if roundKeys[1][unshiftRows(pos)] != b {
t.Fatalf("Constant part of encoding was not key byte!")
}
}
}
// FindPartialEncoding takes an affine encoded F and finds the values that strip its output encoding. It returns the
// parameters it finds and the input encoding of f up to a key byte.
func FindPartialEncoding(constr *chow.Construction, f table.Byte, L, AtildeInv matrix.Matrix) (number.ByteFieldElem, byte, encoding.ByteAffine) {
fInv := table.Invert(f)
id := encoding.ByteLinear(matrix.GenerateIdentity(8))
SInv := table.InvertibleTable(chow.InvTBox{saes.Construction{}, 0x00, 0x00})
S := table.Invert(SInv)
// Brute force the constant part of the output encoding and the beta in Atilde = A_i <- D(beta)
for c := 0; c < 256; c++ {
for d := 1; d < 256; d++ {
cand := encoding.ComposedBytes{
TableAsEncoding{f, fInv},
encoding.ByteAffine{id, byte(c)},
encoding.ByteLinear(AtildeInv),
encoding.ByteMultiplication(byte(d)), // D below
TableAsEncoding{SInv, S},
}
if isAffine(cand) {
a, b := DecomposeAffineEncoding(cand)
return number.ByteFieldElem(d), byte(c), encoding.ByteAffine{encoding.ByteLinear(a), byte(b)}
}
}
}
panic("Failed to strip output encodings!")
}
func generateMask(rs *RandomSource, maskType MaskType, surface Surface) matrix.Matrix {
if maskType == RandomMask {
label := make([]byte, 16)
if surface == Inside {
copy(label[:], []byte("MASK Inside"))
return rs.Matrix(label, 128)
} else {
copy(label[:], []byte("MASK Outside"))
return rs.Matrix(label, 128)
}
} else { // Identity mask.
return matrix.GenerateIdentity(128)
}
}