Wrap hex.DecodeString() into mustDecodeHexString()

The hex decoding is only done from the JSON files provided by the
wycheproof-testvectors package. Failure is always fatal. So there
is no need for repeated error checks, and we can use an ergonomic
wrapper.

Also rework the calculation of the message digest from input data
this had a similar deficit.

All in all this shaves off about 10% of the code and removes a lot
of tedious repetition.

1 files changed, 78 insertions, 390 deletions

diff --git a/regress/lib/libcrypto/wycheproof/wycheproof.go b/regress/lib/libcrypto/wycheproof/wycheproof.go
index 6f33fe56c6a..dea2f2e5f8b 100644
--- a/regress/lib/libcrypto/wycheproof/wycheproof.go
+++ b/regress/lib/libcrypto/wycheproof/wycheproof.go
@@ -1,4 +1,4 @@
-/* $OpenBSD: wycheproof.go,v 1.154 2023/11/07 16:37:02 tb Exp $ */
+/* $OpenBSD: wycheproof.go,v 1.155 2023/11/07 16:46:12 tb Exp $ */
 /*
  * Copyright (c) 2018 Joel Sing <jsing@openbsd.org>
  * Copyright (c) 2018,2019,2022 Theo Buehler <tb@openbsd.org>
@@ -709,24 +709,33 @@ func aeadAes(size int) (*C.EVP_AEAD, error) {
 	return nil, fmt.Errorf("invalid key size: %d", size)
 }
 
-func hashEvpDigestMessage(md *C.EVP_MD, msg []byte) ([]byte, int, error) {
+func mustHashHexMessage(md *C.EVP_MD, message string) ([]byte, int) {
 	size := C.EVP_MD_size(md)
 	if size <= 0 || size > C.EVP_MAX_MD_SIZE {
-		return nil, 0, fmt.Errorf("unexpected MD size %d", size)
+		log.Fatalf("unexpected MD size %d", size)
 	}
 
-	msgLen := len(msg)
-	if msgLen == 0 {
-		msg = append(msg, 0)
-	}
+	msg, msgLen := mustDecodeHexString(message, "for hex message digest")
 
 	digest := make([]byte, size)
 
 	if C.EVP_Digest(unsafe.Pointer(&msg[0]), C.size_t(msgLen), (*C.uchar)(unsafe.Pointer(&digest[0])), nil, md, nil) != 1 {
-		return nil, 0, fmt.Errorf("EVP_Digest failed")
+		log.Fatalf("EVP_Digest failed")
 	}
 
-	return digest, int(size), nil
+	return digest, int(size)
+}
+
+func mustDecodeHexString(str, descr string) (out []byte, outLen int) {
+	out, err := hex.DecodeString(str)
+	if err != nil {
+		log.Fatalf("Failed to decode %s %q: %v", descr, str, err)
+	}
+	outLen = len(out)
+	if outLen == 0 {
+		out = append(out, 0)
+	}
+	return out, outLen
 }
 
 func checkAesCbcPkcs5(ctx *C.EVP_CIPHER_CTX, doEncrypt int, key []byte, keyLen int,
@@ -790,37 +799,10 @@ func checkAesCbcPkcs5(ctx *C.EVP_CIPHER_CTX, doEncrypt int, key []byte, keyLen i
 }
 
 func runAesCbcPkcs5Test(ctx *C.EVP_CIPHER_CTX, wt *wycheproofTestAesCbcPkcs5) bool {
-	key, err := hex.DecodeString(wt.Key)
-	if err != nil {
-		log.Fatalf("Failed to decode key %q: %v", wt.Key, err)
-	}
-	iv, err := hex.DecodeString(wt.IV)
-	if err != nil {
-		log.Fatalf("Failed to decode IV %q: %v", wt.IV, err)
-	}
-	ct, err := hex.DecodeString(wt.CT)
-	if err != nil {
-		log.Fatalf("Failed to decode CT %q: %v", wt.CT, err)
-	}
-	msg, err := hex.DecodeString(wt.Msg)
-	if err != nil {
-		log.Fatalf("Failed to decode message %q: %v", wt.Msg, err)
-	}
-
-	keyLen, ivLen, ctLen, msgLen := len(key), len(iv), len(ct), len(msg)
-
-	if keyLen == 0 {
-		key = append(key, 0)
-	}
-	if ivLen == 0 {
-		iv = append(iv, 0)
-	}
-	if ctLen == 0 {
-		ct = append(ct, 0)
-	}
-	if msgLen == 0 {
-		msg = append(msg, 0)
-	}
+	key, keyLen := mustDecodeHexString(wt.Key, "key")
+	iv, ivLen := mustDecodeHexString(wt.IV, "iv")
+	ct, ctLen := mustDecodeHexString(wt.CT, "ct")
+	msg, msgLen := mustDecodeHexString(wt.Msg, "message")
 
 	openSuccess := checkAesCbcPkcs5(ctx, 0, key, keyLen, iv, ivLen, ct, ctLen, msg, msgLen, wt)
 	sealSuccess := checkAesCbcPkcs5(ctx, 1, key, keyLen, iv, ivLen, msg, msgLen, ct, ctLen, wt)
@@ -997,56 +979,12 @@ func checkAesAead(algorithm string, ctx *C.EVP_CIPHER_CTX, doEncrypt int,
 }
 
 func runAesAeadTest(algorithm string, ctx *C.EVP_CIPHER_CTX, aead *C.EVP_AEAD, wt *wycheproofTestAead) bool {
-	key, err := hex.DecodeString(wt.Key)
-	if err != nil {
-		log.Fatalf("Failed to decode key %q: %v", wt.Key, err)
-	}
-
-	iv, err := hex.DecodeString(wt.IV)
-	if err != nil {
-		log.Fatalf("Failed to decode IV %q: %v", wt.IV, err)
-	}
-
-	aad, err := hex.DecodeString(wt.AAD)
-	if err != nil {
-		log.Fatalf("Failed to decode AAD %q: %v", wt.AAD, err)
-	}
-
-	msg, err := hex.DecodeString(wt.Msg)
-	if err != nil {
-		log.Fatalf("Failed to decode msg %q: %v", wt.Msg, err)
-	}
-
-	ct, err := hex.DecodeString(wt.CT)
-	if err != nil {
-		log.Fatalf("Failed to decode CT %q: %v", wt.CT, err)
-	}
-
-	tag, err := hex.DecodeString(wt.Tag)
-	if err != nil {
-		log.Fatalf("Failed to decode tag %q: %v", wt.Tag, err)
-	}
-
-	keyLen, ivLen, aadLen, msgLen, ctLen, tagLen := len(key), len(iv), len(aad), len(msg), len(ct), len(tag)
-
-	if keyLen == 0 {
-		key = append(key, 0)
-	}
-	if ivLen == 0 {
-		iv = append(iv, 0)
-	}
-	if aadLen == 0 {
-		aad = append(aad, 0)
-	}
-	if msgLen == 0 {
-		msg = append(msg, 0)
-	}
-	if ctLen == 0 {
-		ct = append(ct, 0)
-	}
-	if tagLen == 0 {
-		tag = append(tag, 0)
-	}
+	key, keyLen := mustDecodeHexString(wt.Key, "key")
+	iv, ivLen := mustDecodeHexString(wt.IV, "iv")
+	aad, aadLen := mustDecodeHexString(wt.AAD, "aad")
+	msg, msgLen := mustDecodeHexString(wt.Msg, "msg")
+	ct, ctLen := mustDecodeHexString(wt.CT, "CT")
+	tag, tagLen := mustDecodeHexString(wt.Tag, "tag")
 
 	openEvp := checkAesAead(algorithm, ctx, 0, key, keyLen, iv, ivLen, aad, aadLen, ct, ctLen, msg, msgLen, tag, tagLen, wt)
 	sealEvp := checkAesAead(algorithm, ctx, 1, key, keyLen, iv, ivLen, aad, aadLen, msg, msgLen, ct, ctLen, tag, tagLen, wt)
@@ -1110,32 +1048,9 @@ func (wtg *wycheproofTestGroupAesAead) run(algorithm string, variant testVariant
 }
 
 func runAesCmacTest(cipher *C.EVP_CIPHER, wt *wycheproofTestAesCmac) bool {
-	key, err := hex.DecodeString(wt.Key)
-	if err != nil {
-		log.Fatalf("Failed to decode key %q: %v", wt.Key, err)
-	}
-
-	msg, err := hex.DecodeString(wt.Msg)
-	if err != nil {
-		log.Fatalf("Failed to decode msg %q: %v", wt.Msg, err)
-	}
-
-	tag, err := hex.DecodeString(wt.Tag)
-	if err != nil {
-		log.Fatalf("Failed to decode tag %q: %v", wt.Tag, err)
-	}
-
-	keyLen, msgLen, tagLen := len(key), len(msg), len(tag)
-
-	if keyLen == 0 {
-		key = append(key, 0)
-	}
-	if msgLen == 0 {
-		msg = append(msg, 0)
-	}
-	if tagLen == 0 {
-		tag = append(tag, 0)
-	}
+	key, keyLen := mustDecodeHexString(wt.Key, "key")
+	msg, msgLen := mustDecodeHexString(wt.Msg, "msg")
+	tag, tagLen := mustDecodeHexString(wt.Tag, "tag")
 
 	mdctx := C.EVP_MD_CTX_new()
 	if mdctx == nil {
@@ -1291,22 +1206,13 @@ func runChaCha20Poly1305Test(algorithm string, wt *wycheproofTestAead) bool {
 		aead = C.EVP_aead_xchacha20_poly1305()
 	}
 
-	key, err := hex.DecodeString(wt.Key)
-	if err != nil {
-		log.Fatalf("Failed to decode key %q: %v", wt.Key, err)
-	}
-	iv, err := hex.DecodeString(wt.IV)
-	if err != nil {
-		log.Fatalf("Failed to decode key %q: %v", wt.IV, err)
-	}
-	aad, err := hex.DecodeString(wt.AAD)
-	if err != nil {
-		log.Fatalf("Failed to decode AAD %q: %v", wt.AAD, err)
-	}
-	msg, err := hex.DecodeString(wt.Msg)
-	if err != nil {
-		log.Fatalf("Failed to decode msg %q: %v", wt.Msg, err)
-	}
+	key, keyLen := mustDecodeHexString(wt.Key, "key")
+	ct, ctLen := mustDecodeHexString(wt.CT, "CT")
+	iv, ivLen := mustDecodeHexString(wt.IV, "iv")
+	aad, aadLen := mustDecodeHexString(wt.AAD, "aad")
+	msg, msgLen := mustDecodeHexString(wt.Msg, "msg")
+
+	// ct and tag are concatenated in checkAeadOpen(), so don't use mustDecodeHexString()
 	ct, err := hex.DecodeString(wt.CT)
 	if err != nil {
 		log.Fatalf("Failed to decode ct %q: %v", wt.CT, err)
@@ -1315,18 +1221,7 @@ func runChaCha20Poly1305Test(algorithm string, wt *wycheproofTestAead) bool {
 	if err != nil {
 		log.Fatalf("Failed to decode tag %q: %v", wt.Tag, err)
 	}
-
-	keyLen, ivLen, aadLen, msgLen, ctLen, tagLen := len(key), len(iv), len(aad), len(msg), len(ct), len(tag)
-
-	if ivLen == 0 {
-		iv = append(iv, 0)
-	}
-	if aadLen == 0 {
-		aad = append(aad, 0)
-	}
-	if msgLen == 0 {
-		msg = append(msg, 0)
-	}
+	ctLen, tagLen := len(ct), len(tag)
 
 	ctx := C.EVP_AEAD_CTX_new()
 	if ctx == nil {
@@ -1410,15 +1305,7 @@ func encodeDSAP1363Sig(wtSig string) (*C.uchar, C.int) {
 }
 
 func runDSATest(dsa *C.DSA, md *C.EVP_MD, variant testVariant, wt *wycheproofTestDSA) bool {
-	msg, err := hex.DecodeString(wt.Msg)
-	if err != nil {
-		log.Fatalf("Failed to decode message %q: %v", wt.Msg, err)
-	}
-
-	msg, msgLen, err := hashEvpDigestMessage(md, msg)
-	if err != nil {
-		log.Fatalf("%v", err)
-	}
+	msg, msgLen := mustHashHexMessage(md, wt.Msg)
 
 	var ret C.int
 	if variant == P1363 {
@@ -1432,14 +1319,7 @@ func runDSATest(dsa *C.DSA, md *C.EVP_MD, variant testVariant, wt *wycheproofTes
 		ret = C.DSA_verify(0, (*C.uchar)(unsafe.Pointer(&msg[0])), C.int(msgLen),
 			(*C.uchar)(unsafe.Pointer(cDer)), C.int(derLen), dsa)
 	} else {
-		sig, err := hex.DecodeString(wt.Sig)
-		if err != nil {
-			log.Fatalf("Failed to decode signature %q: %v", wt.Sig, err)
-		}
-		sigLen := len(sig)
-		if sigLen == 0 {
-			sig = append(msg, 0)
-		}
+		sig, sigLen := mustDecodeHexString(wt.Sig, "sig")
 		ret = C.DSA_verify(0, (*C.uchar)(unsafe.Pointer(&msg[0])), C.int(msgLen),
 			(*C.uchar)(unsafe.Pointer(&sig[0])), C.int(sigLen), dsa)
 	}
@@ -1505,15 +1385,7 @@ func (wtg *wycheproofTestGroupDSA) run(algorithm string, variant testVariant) bo
 		log.Fatalf("Failed to get hash: %v", err)
 	}
 
-	der, err := hex.DecodeString(wtg.KeyDER)
-	if err != nil {
-		log.Fatalf("Failed to decode DER encoded key: %v", err)
-	}
-
-	derLen := len(der)
-	if derLen == 0 {
-		der = append(der, 0)
-	}
+	der, derLen := mustDecodeHexString(wtg.KeyDER, "DER encoded key")
 
 	Cder := (*C.uchar)(C.malloc(C.ulong(derLen)))
 	if Cder == nil {
@@ -1576,15 +1448,7 @@ func runECDHTest(nid int, variant testVariant, wt *wycheproofTestECDH) bool {
 		return false
 	}
 
-	pub, err := hex.DecodeString(wt.Public)
-	if err != nil {
-		log.Fatalf("Failed to decode public key: %v", err)
-	}
-
-	pubLen := len(pub)
-	if pubLen == 0 {
-		pub = append(pub, 0)
-	}
+	pub, pubLen := mustDecodeHexString(wt.Public, "public key")
 
 	Cpub := (*C.uchar)(C.malloc(C.ulong(pubLen)))
 	if Cpub == nil {
@@ -1634,13 +1498,10 @@ func runECDHTest(nid int, variant testVariant, wt *wycheproofTestECDH) bool {
 		return false
 	}
 
-	shared, err := hex.DecodeString(wt.Shared)
-	if err != nil {
-		log.Fatalf("Failed to decode shared secret: %v", err)
-	}
+	shared, sharedLen := mustDecodeHexString(wt.Shared, "shared secret")
 
 	// XXX The shared fields of the secp224k1 test cases have a 0 byte preprended.
-	if len(shared) == int(secLen)+1 && shared[0] == 0 {
+	if sharedLen == int(secLen)+1 && shared[0] == 0 {
 		fmt.Printf("INFO: %s - prepending 0 byte.\n", wt)
 		// shared = shared[1:];
 		zero := make([]byte, 1, secLen+1)
@@ -1750,10 +1611,7 @@ func runECDHWebCryptoTest(nid int, wt *wycheproofTestECDHWebCrypto) bool {
 		return false
 	}
 
-	shared, err := hex.DecodeString(wt.Shared)
-	if err != nil {
-		log.Fatalf("Failed to decode shared secret: %v", err)
-	}
+	shared, _ := mustDecodeHexString(wt.Shared, "shared secret")
 
 	success := true
 	if !bytes.Equal(shared, secret) {
@@ -1782,15 +1640,7 @@ func (wtg *wycheproofTestGroupECDHWebCrypto) run(algorithm string, variant testV
 }
 
 func runECDSATest(ecKey *C.EC_KEY, md *C.EVP_MD, nid int, variant testVariant, wt *wycheproofTestECDSA) bool {
-	msg, err := hex.DecodeString(wt.Msg)
-	if err != nil {
-		log.Fatalf("Failed to decode message %q: %v", wt.Msg, err)
-	}
-
-	msg, msgLen, err := hashEvpDigestMessage(md, msg)
-	if err != nil {
-		log.Fatalf("%v", err)
-	}
+	msg, msgLen := mustHashHexMessage(md, wt.Msg)
 
 	var ret C.int
 	if variant == Webcrypto || variant == P1363 {
@@ -1804,15 +1654,8 @@ func runECDSATest(ecKey *C.EC_KEY, md *C.EVP_MD, nid int, variant testVariant, w
 		ret = C.ECDSA_verify(0, (*C.uchar)(unsafe.Pointer(&msg[0])), C.int(msgLen),
 			(*C.uchar)(unsafe.Pointer(cDer)), C.int(derLen), ecKey)
 	} else {
-		sig, err := hex.DecodeString(wt.Sig)
-		if err != nil {
-			log.Fatalf("Failed to decode signature %q: %v", wt.Sig, err)
-		}
+		sig, sigLen := mustDecodeHexString(wt.Sig, "sig")
 
-		sigLen := len(sig)
-		if sigLen == 0 {
-			sig = append(sig, 0)
-		}
 		ret = C.ECDSA_verify(0, (*C.uchar)(unsafe.Pointer(&msg[0])), C.int(msgLen),
 			(*C.uchar)(unsafe.Pointer(&sig[0])), C.int(sigLen), ecKey)
 	}
@@ -1993,23 +1836,8 @@ func runEdDSATest(pkey *C.EVP_PKEY, wt *wycheproofTestEdDSA) bool {
 		log.Fatal("EVP_DigestVerifyInit failed")
 	}
 
-	msg, err := hex.DecodeString(wt.Msg)
-	if err != nil {
-		log.Fatalf("Failed to decode Message %q: %v", wt.Msg, err)
-	}
-	msgLen := len(msg)
-	if msgLen == 0 {
-		msg = append(msg, 0)
-	}
-
-	sig, err := hex.DecodeString(wt.Sig)
-	if err != nil {
-		log.Fatalf("Failed to decode Signature %q: %v", wt.Sig, err)
-	}
-	sigLen := len(sig)
-	if sigLen == 0 {
-		sig = append(sig, 0)
-	}
+	msg, msgLen := mustDecodeHexString(wt.Msg, "msg")
+	sig, sigLen := mustDecodeHexString(wt.Sig, "sig")
 
 	ret := C.EVP_DigestVerify(mdctx, (*C.uchar)(unsafe.Pointer(&sig[0])), (C.size_t)(sigLen), (*C.uchar)(unsafe.Pointer(&msg[0])), (C.size_t)(msgLen))
 
@@ -2029,12 +1857,9 @@ func (wtg *wycheproofTestGroupEdDSA) run(algorithm string, variant testVariant)
 		return false
 	}
 
-	pubKey, err := hex.DecodeString(wtg.Key.Pk)
-	if err != nil {
-		log.Fatalf("Failed to decode Pubkey %q: %v", wtg.Key.Pk, err)
-	}
+	pubKey, pubKeyLen := mustDecodeHexString(wtg.Key.Pk, "pubkey")
 
-	pkey := C.EVP_PKEY_new_raw_public_key(C.EVP_PKEY_ED25519, nil, (*C.uchar)(unsafe.Pointer(&pubKey[0])), (C.size_t)(len(pubKey)))
+	pkey := C.EVP_PKEY_new_raw_public_key(C.EVP_PKEY_ED25519, nil, (*C.uchar)(unsafe.Pointer(&pubKey[0])), (C.size_t)(pubKeyLen))
 	if pkey == nil {
 		log.Fatal("EVP_PKEY_new_raw_public_key failed")
 	}
@@ -2050,29 +1875,9 @@ func (wtg *wycheproofTestGroupEdDSA) run(algorithm string, variant testVariant)
 }
 
 func runHkdfTest(md *C.EVP_MD, wt *wycheproofTestHkdf) bool {
-	ikm, err := hex.DecodeString(wt.Ikm)
-	if err != nil {
-		log.Fatalf("Failed to decode ikm %q: %v", wt.Ikm, err)
-	}
-	salt, err := hex.DecodeString(wt.Salt)
-	if err != nil {
-		log.Fatalf("Failed to decode salt %q: %v", wt.Salt, err)
-	}
-	info, err := hex.DecodeString(wt.Info)
-	if err != nil {
-		log.Fatalf("Failed to decode info %q: %v", wt.Info, err)
-	}
-
-	ikmLen, saltLen, infoLen := len(ikm), len(salt), len(info)
-	if ikmLen == 0 {
-		ikm = append(ikm, 0)
-	}
-	if saltLen == 0 {
-		salt = append(salt, 0)
-	}
-	if infoLen == 0 {
-		info = append(info, 0)
-	}
+	ikm, ikmLen := mustDecodeHexString(wt.Ikm, "ikm")
+	salt, saltLen := mustDecodeHexString(wt.Salt, "salt")
+	info, infoLen := mustDecodeHexString(wt.Info, "info")
 
 	outLen := wt.Size
 	out := make([]byte, outLen)
@@ -2120,10 +1925,7 @@ func runHkdfTest(md *C.EVP_MD, wt *wycheproofTestHkdf) bool {
 		return success
 	}
 
-	okm, err := hex.DecodeString(wt.Okm)
-	if err != nil {
-		log.Fatalf("Failed to decode okm %q: %v", wt.Okm, err)
-	}
+	okm, _ := mustDecodeHexString(wt.Okm, "okm")
 	if !bytes.Equal(out[:outLen], okm) {
 		fmt.Printf("FAIL: %s - expected and computed output don't match.\n", wt)
 	}
@@ -2148,25 +1950,8 @@ func (wtg *wycheproofTestGroupHkdf) run(algorithm string, variant testVariant) b
 }
 
 func runHmacTest(md *C.EVP_MD, tagBytes int, wt *wycheproofTestHmac) bool {
-	key, err := hex.DecodeString(wt.Key)
-	if err != nil {
-		log.Fatalf("failed to decode key %q: %v", wt.Key, err)
-	}
-
-	msg, err := hex.DecodeString(wt.Msg)
-	if err != nil {
-		log.Fatalf("failed to decode msg %q: %v", wt.Msg, err)
-	}
-
-	keyLen, msgLen := len(key), len(msg)
-
-	if keyLen == 0 {
-		key = append(key, 0)
-	}
-
-	if msgLen == 0 {
-		msg = append(msg, 0)
-	}
+	key, keyLen := mustDecodeHexString(wt.Key, "key")
+	msg, msgLen := mustDecodeHexString(wt.Msg, "msg")
 
 	got := make([]byte, C.EVP_MAX_MD_SIZE)
 	var gotLen C.uint
@@ -2187,11 +1972,7 @@ func runHmacTest(md *C.EVP_MD, tagBytes int, wt *wycheproofTestHmac) bool {
 		return false
 	}
 
-	tag, err := hex.DecodeString(wt.Tag)
-	if err != nil {
-		log.Fatalf("failed to decode tag %q: %v", wt.Tag, err)
-	}
-
+	tag, _ := mustDecodeHexString(wt.Tag, "tag")
 	success = bytes.Equal(got[:tagBytes], tag) == (wt.Result == "valid")
 
 	if !success {
@@ -2279,30 +2060,9 @@ func runKWTestUnWrap(keySize int, key []byte, keyLen int, msg []byte, msgLen int
 }
 
 func runKWTest(keySize int, wt *wycheproofTestKW) bool {
-	key, err := hex.DecodeString(wt.Key)
-	if err != nil {
-		log.Fatalf("Failed to decode key %q: %v", wt.Key, err)
-	}
-	msg, err := hex.DecodeString(wt.Msg)
-	if err != nil {
-		log.Fatalf("Failed to decode msg %q: %v", wt.Msg, err)
-	}
-	ct, err := hex.DecodeString(wt.CT)
-	if err != nil {
-		log.Fatalf("Failed to decode ct %q: %v", wt.CT, err)
-	}
-
-	keyLen, msgLen, ctLen := len(key), len(msg), len(ct)
-
-	if keyLen == 0 {
-		key = append(key, 0)
-	}
-	if msgLen == 0 {
-		msg = append(msg, 0)
-	}
-	if ctLen == 0 {
-		ct = append(ct, 0)
-	}
+	key, keyLen := mustDecodeHexString(wt.Key, "key")
+	msg, msgLen := mustDecodeHexString(wt.Msg, "msg")
+	ct, ctLen := mustDecodeHexString(wt.CT, "CT")
 
 	wrapSuccess := runKWTestWrap(keySize, key, keyLen, msg, msgLen, ct, ctLen, wt)
 	unwrapSuccess := runKWTestUnWrap(keySize, key, keyLen, msg, msgLen, ct, ctLen, wt)
@@ -2353,14 +2113,7 @@ func (wtg *wycheproofTestGroupPrimality) run(algorithm string, variant testVaria
 }
 
 func runRsaesOaepTest(rsa *C.RSA, sha *C.EVP_MD, mgfSha *C.EVP_MD, wt *wycheproofTestRsaes) bool {
-	ct, err := hex.DecodeString(wt.CT)
-	if err != nil {
-		log.Fatalf("Failed to decode cipher text %q: %v", wt.CT, err)
-	}
-	ctLen := len(ct)
-	if ctLen == 0 {
-		ct = append(ct, 0)
-	}
+	ct, ctLen := mustDecodeHexString(wt.CT, "CT")
 
 	rsaSize := C.RSA_size(rsa)
 	decrypted := make([]byte, rsaSize)
@@ -2378,20 +2131,8 @@ func runRsaesOaepTest(rsa *C.RSA, sha *C.EVP_MD, mgfSha *C.EVP_MD, wt *wycheproo
 		return success
 	}
 
-	label, err := hex.DecodeString(wt.Label)
-	if err != nil {
-		log.Fatalf("Failed to decode label %q: %v", wt.Label, err)
-	}
-	labelLen := len(label)
-	if labelLen == 0 {
-		label = append(label, 0)
-	}
-
-	msg, err := hex.DecodeString(wt.Msg)
-	if err != nil {
-		log.Fatalf("Failed to decode message %q: %v", wt.Msg, err)
-	}
-	msgLen := len(msg)
+	label, labelLen := mustDecodeHexString(wt.Label, "label")
+	msg, msgLen := mustDecodeHexString(wt.Msg, "msg")
 
 	to := make([]byte, rsaSize)
 
@@ -2407,7 +2148,7 @@ func runRsaesOaepTest(rsa *C.RSA, sha *C.EVP_MD, mgfSha *C.EVP_MD, wt *wycheproo
 	}
 
 	to = to[:msgLen]
-	if !bytes.Equal(msg, to) {
+	if !bytes.Equal(msg[:msgLen], to) {
 		success = false
 		fmt.Printf("FAIL: %s - expected and calculated message differ.\n", wt)
 	}
@@ -2476,14 +2217,7 @@ func (wtg *wycheproofTestGroupRsaesOaep) run(algorithm string, variant testVaria
 }
 
 func runRsaesPkcs1Test(rsa *C.RSA, wt *wycheproofTestRsaes) bool {
-	ct, err := hex.DecodeString(wt.CT)
-	if err != nil {
-		log.Fatalf("Failed to decode cipher text %q: %v", wt.CT, err)
-	}
-	ctLen := len(ct)
-	if ctLen == 0 {
-		ct = append(ct, 0)
-	}
+	ct, ctLen := mustDecodeHexString(wt.CT, "CT")
 
 	rsaSize := C.RSA_size(rsa)
 	decrypted := make([]byte, rsaSize)
@@ -2501,15 +2235,12 @@ func runRsaesPkcs1Test(rsa *C.RSA, wt *wycheproofTestRsaes) bool {
 		return success
 	}
 
-	msg, err := hex.DecodeString(wt.Msg)
-	if err != nil {
-		log.Fatalf("Failed to decode message %q: %v", wt.Msg, err)
-	}
+	msg, msgLen := mustDecodeHexString(wt.Msg, "msg")
 
-	if int(ret) != len(msg) {
+	if int(ret) != msgLen {
 		success = false
-		fmt.Printf("FAIL: %s - got %d, want %d.\n", wt, ret, len(msg))
-	} else if !bytes.Equal(msg, decrypted[:len(msg)]) {
+		fmt.Printf("FAIL: %s - got %d, want %d\n", wt, ret, len(msg))
+	} else if !bytes.Equal(msg[:msgLen], decrypted[:msgLen]) {
 		success = false
 		fmt.Printf("FAIL: %s - expected and calculated message differ.\n", wt)
 	}
@@ -2566,25 +2297,8 @@ func (wtg *wycheproofTestGroupRsaesPkcs1) run(algorithm string, variant testVari
 }
 
 func runRsassaTest(rsa *C.RSA, sha *C.EVP_MD, mgfSha *C.EVP_MD, sLen int, wt *wycheproofTestRsassa) bool {
-	msg, err := hex.DecodeString(wt.Msg)
-	if err != nil {
-		log.Fatalf("Failed to decode message %q: %v", wt.Msg, err)
-	}
-
-	msg, _, err = hashEvpDigestMessage(sha, msg)
-	if err != nil {
-		log.Fatalf("%v", err)
-	}
-
-	sig, err := hex.DecodeString(wt.Sig)
-	if err != nil {
-		log.Fatalf("Failed to decode signature %q: %v", wt.Sig, err)
-	}
-
-	sigLen := len(sig)
-	if sigLen == 0 {
-		sig = append(sig, 0)
-	}
+	msg, _ := mustHashHexMessage(sha, wt.Msg)
+	sig, sigLen := mustDecodeHexString(wt.Sig, "sig")
 
 	sigOut := make([]byte, C.RSA_size(rsa)-11)
 	if sigLen == 0 {
@@ -2668,25 +2382,8 @@ func (wtg *wycheproofTestGroupRsassa) run(algorithm string, variant testVariant)
 }
 
 func runRSATest(rsa *C.RSA, md *C.EVP_MD, nid int, wt *wycheproofTestRSA) bool {
-	msg, err := hex.DecodeString(wt.Msg)
-	if err != nil {
-		log.Fatalf("Failed to decode message %q: %v", wt.Msg, err)
-	}
-
-	msg, msgLen, err := hashEvpDigestMessage(md, msg)
-	if err != nil {
-		log.Fatalf("%v", err)
-	}
-
-	sig, err := hex.DecodeString(wt.Sig)
-	if err != nil {
-		log.Fatalf("Failed to decode signature %q: %v", wt.Sig, err)
-	}
-
-	sigLen := len(sig)
-	if sigLen == 0 {
-		sig = append(sig, 0)
-	}
+	msg, msgLen := mustHashHexMessage(md, wt.Msg)
+	sig, sigLen := mustDecodeHexString(wt.Sig, "sig")
 
 	ret := C.RSA_verify(C.int(nid), (*C.uchar)(unsafe.Pointer(&msg[0])), C.uint(msgLen),
 		(*C.uchar)(unsafe.Pointer(&sig[0])), C.uint(sigLen), rsa)
@@ -2751,18 +2448,9 @@ func (wtg *wycheproofTestGroupRSA) run(algorithm string, variant testVariant) bo
 }
 
 func runX25519Test(wt *wycheproofTestX25519) bool {
-	public, err := hex.DecodeString(wt.Public)
-	if err != nil {
-		log.Fatalf("Failed to decode public %q: %v", wt.Public, err)
-	}
-	private, err := hex.DecodeString(wt.Private)
-	if err != nil {
-		log.Fatalf("Failed to decode private %q: %v", wt.Private, err)
-	}
-	shared, err := hex.DecodeString(wt.Shared)
-	if err != nil {
-		log.Fatalf("Failed to decode shared %q: %v", wt.Shared, err)
-	}
+	public, _ := mustDecodeHexString(wt.Public, "public")
+	private, _ := mustDecodeHexString(wt.Private, "private")
+	shared, _ := mustDecodeHexString(wt.Shared, "shared")
 
 	got := make([]byte, C.X25519_KEY_LENGTH)
 	result := true