Widen FPSAP exchange coverage to 151 vectors

internal/airplay/fpsap_corpus_test.go

@@ -0,0 +1,95 @@
+package airplay
+
+import (
+	"crypto/sha256"
+	"testing"
+)
+
+// fpsapCorpusPayloads builds a deterministic set of 128-byte challenge bodies:
+// structural edge cases first -- block boundaries, single bits, all-ones with
+// one byte cleared -- then a pseudorandom tail from the same xorshift generator
+// TestFairPlaySAPHashCorpus uses.
+func fpsapCorpusPayloads() [][128]byte {
+	var out [][128]byte
+	add := func(p [128]byte) { out = append(out, p) }
+
+	var zero [128]byte
+	add(zero)
+
+	for _, v := range []byte{0x01, 0x42, 0x55, 0x7f, 0x80, 0xaa, 0xff} {
+		var p [128]byte
+		for i := range p {
+			p[i] = v
+		}
+		add(p)
+	}
+
+	for _, s := range []byte{0x00, 0x40, 0x80, 0xc0} {
+		var p [128]byte
+		for i := range p {
+			p[i] = s + byte(i)
+		}
+		add(p)
+	}
+
+	// One byte set, on and around every 16-byte block boundary.
+	for _, idx := range []int{0, 1, 2, 15, 16, 31, 32, 63, 64, 95, 96, 126, 127} {
+		for _, v := range []byte{0x01, 0x80, 0xff} {
+			var p [128]byte
+			p[idx] = v
+			add(p)
+		}
+	}
+
+	// One bit set in each of the eight blocks.
+	for blk := 0; blk < 8; blk++ {
+		for bit := 0; bit < 8; bit++ {
+			var p [128]byte
+			p[blk*16] = 1 << bit
+			add(p)
+		}
+	}
+
+	for _, idx := range []int{0, 63, 64, 127} {
+		var p [128]byte
+		for i := range p {
+			p[i] = 0xff
+		}
+		p[idx] = 0
+		add(p)
+	}
+
+	var state uint64 = 0x6a09e667f3bcc909
+	for range 32 {
+		var p [128]byte
+		for i := range p {
+			state ^= state << 13
+			state ^= state >> 7
+			state ^= state << 17
+			p[i] = byte(state)
+		}
+		add(p)
+	}
+
+	return out
+}
+
+// TestFPSAPExchangeCorpus widens the exchange coverage from the seven vectors in
+// TestFPSAPExchangeGoldenVectors to 151.
+//
+// The expected aggregate was produced by a separate, independently derived
+// implementation of this exchange, not by this package -- so it checks the two
+// against each other rather than checking this package against itself.
+func TestFPSAPExchangeCorpus(t *testing.T) {
+	corpusHash := sha256.New()
+	payloads := fpsapCorpusPayloads()
+	for _, payload := range payloads {
+		digest := fpsapExchangeForSAP(fpsapReferenceLocalSAP(), mustDecryptFPSAPBody(t, 3, payload))
+		_, _ = corpusHash.Write(digest[:])
+	}
+	if len(payloads) != 151 {
+		t.Fatalf("corpus length = %d, want 151", len(payloads))
+	}
+	requireFairPlayHex(t, "FPSAP exchange corpus", corpusHash.Sum(nil),
+		"68f4a4d3ad5603fc569ee7deb013d3a5de91d7590274272a16750fe02370fd9d")
+}