Merge branch 'onion'

Makefile

@@ -33,6 +33,7 @@ TEST_CLI_PROGRAMS :=				\
 
 TEST_PROGRAMS :=				\
 	test/test_state_coverage		\
+	test/onion_key				\
 	test/test_onion
 
 BITCOIN_OBJS :=					\
@@ -99,8 +100,17 @@ test-cli-tests: $(TEST_CLI_PROGRAMS)
 	cd test-cli; scripts/shutdown.sh 2>/dev/null || true
 	set -e; cd test-cli; for args in "" --steal --unilateral --htlc-onchain; do scripts/setup.sh && scripts/test.sh $$args && scripts/shutdown.sh; done
 
-test-onion: test/test_onion
-	set -e; for i in `seq 20`; do ./test/test_onion $$i; done
+test-onion: test/test_onion test/onion_key
+	set -e; TMPF=/tmp/onion.$$$$; test/test_onion --generate $$(test/onion_key --pub `seq 20`) > $$TMPF; for k in `seq 20`; do test/test_onion --decode $$(test/onion_key --priv $$k) < $$TMPF > $$TMPF.unwrap; mv $$TMPF.unwrap $$TMPF; done; rm -f $$TMPF
+
+test-onion2: test/test_onion test/onion_key
+	set -e; TMPF=/tmp/onion.$$$$; python test/test_onion.py generate $$(test/onion_key --pub `seq 20`) > $$TMPF; for k in `seq 20`; do test/test_onion --decode $$(test/onion_key --priv $$k) < $$TMPF > $$TMPF.unwrap; mv $$TMPF.unwrap $$TMPF; done; rm -f $$TMPF
+
+test-onion3: test/test_onion test/onion_key
+	set -e; TMPF=/tmp/onion.$$$$; test/test_onion --generate $$(test/onion_key --pub `seq 20`) > $$TMPF; for k in `seq 20`; do python test/test_onion.py decode $$(test/onion_key --priv $$k) $$(test/onion_key --pub $$k) < $$TMPF > $$TMPF.unwrap; mv $$TMPF.unwrap $$TMPF; done; rm -f $$TMPF
+
+test-onion4: test/test_onion test/onion_key
+	set -e; TMPF=/tmp/onion.$$$$; python test/test_onion.py generate $$(test/onion_key --pub `seq 20`) > $$TMPF; for k in `seq 20`; do python test/test_onion.py decode $$(test/onion_key --priv $$k) $$(test/onion_key --pub $$k) < $$TMPF > $$TMPF.unwrap; mv $$TMPF.unwrap $$TMPF; done; rm -f $$TMPF
 
 check: test-cli-tests test-onion
 

test/.gitignore

@@ -0,0 +1,3 @@
+test_onion
+test_state_coverage
+onion_key

test/onion_key.c

@@ -0,0 +1,102 @@
+#define _GNU_SOURCE 1
+#include "secp256k1.h"
+#include "secp256k1_ecdh.h"
+#include "onion_key.h"
+#include "version.h"
+#include <time.h>
+#include <ccan/str/hex/hex.h>
+#include <ccan/opt/opt.h>
+#include <assert.h>
+#include <string.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+/* Not really! */
+static void random_bytes(void *dst, size_t n)
+{
+	size_t i;
+	unsigned char *d = dst;
+
+	for (i = 0; i < n; i++)
+		d[i] = random() % 256;
+}
+
+static void random_key(secp256k1_context *ctx,
+		       struct seckey *seckey, secp256k1_pubkey *pkey)
+{
+	do {
+		random_bytes(seckey->u.u8, sizeof(seckey->u));
+	} while (!secp256k1_ec_pubkey_create(ctx, pkey, seckey->u.u8));
+}
+
+/* We don't want to spend a byte encoding sign, so make sure it's 0x2 */
+static void gen_keys(secp256k1_context *ctx,
+		     struct seckey *seckey, struct compressed_pubkey *pubkey)
+{
+	secp256k1_pubkey pkey;
+	size_t len;
+
+	random_key(ctx, seckey, &pkey);
+
+	secp256k1_ec_pubkey_serialize(ctx, pubkey->u8, &len, &pkey,
+				      SECP256K1_EC_COMPRESSED);
+	assert(len == sizeof(pubkey->u8));
+}
+
+void print_keypair(bool pub, bool priv)
+{
+	secp256k1_context *ctx;
+	struct seckey seckey;
+	struct compressed_pubkey pubkey;
+	char sechex[hex_str_size(sizeof(seckey))];
+	char pubhex[hex_str_size(sizeof(pubkey))];
+
+	assert(pub || priv);
+
+	ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
+	gen_keys(ctx, &seckey, &pubkey);
+
+	hex_encode(&seckey, sizeof(seckey), sechex, sizeof(sechex));
+	hex_encode(&pubkey, sizeof(pubkey), pubhex, sizeof(pubhex));
+
+	if (pub && priv) {
+		printf("%s:%s\n", sechex, pubhex);
+	} else {
+		printf("%s\n", (priv ? sechex : pubhex));
+	}
+}
+
+int main(int argc, char *argv[])
+{
+	bool pub = true, priv = true;
+
+	opt_register_noarg("--help|-h", opt_usage_and_exit,
+			   "[<seeds>...]\n"
+			   "Generate (deterministic if seed) secp256k1 keys",
+			   "Print this message.");
+	opt_register_noarg("--pub",
+			   opt_set_invbool, &priv,
+			   "Generate only the public key");
+	opt_register_noarg("--priv",
+			   opt_set_invbool, &pub,
+			   "Generate only the private key");
+	opt_register_version();
+
+ 	opt_parse(&argc, argv, opt_log_stderr_exit);
+	if (!priv && !pub)
+		opt_usage_exit_fail("Can't use --pub and --priv");
+	
+	if (argc == 1) {
+		srandom(time(NULL) + getpid());
+		print_keypair(pub, priv);
+	} else {
+		int i;
+		for (i = 1; i < argc; i++) {
+			srandom(atoi(argv[i]));
+			print_keypair(pub, priv);
+		}
+	}
+
+	return 0;
+}

test/onion_key.h

@@ -0,0 +1,24 @@
+#ifndef ONION_KEY_H
+#define ONION_KEY_H
+#include <ccan/endian/endian.h>
+#include "bitcoin/privkey.h"
+
+struct seckey {
+	union {
+		struct privkey k;
+		unsigned char u8[32];
+		beint64_t be64[4];
+	} u;
+};
+
+/* First byte is 0x02 or 0x03 indicating even or odd y */
+struct compressed_pubkey {
+	unsigned char u8[33];
+};
+
+/* Prepend 0x02 to get pubkey for libsecp256k1 */
+struct onion_pubkey {
+	unsigned char u8[32];
+};
+
+#endif /* ONION_KEY_H */

test/test_onion.c

@@ -1,6 +1,8 @@
 #define _GNU_SOURCE 1
+#include "onion_key.h"
 #include "secp256k1.h"
 #include "secp256k1_ecdh.h"
+#include "version.h"
 #include <openssl/hmac.h>
 #include <openssl/evp.h>
 #include <openssl/aes.h>
@@ -10,9 +12,14 @@
 #include <err.h>
 #include <stdbool.h>
 #include <assert.h>
+#include <ccan/build_assert/build_assert.h>
 #include <ccan/tal/tal.h>
 #include <ccan/mem/mem.h>
 #include <ccan/crypto/sha256/sha256.h>
+#include <ccan/endian/endian.h>
+#include <ccan/read_write_all/read_write_all.h>
+#include <ccan/opt/opt.h>
+#include <ccan/str/hex/hex.h>
 
 /* 
  * The client knows the server's public key S (which has corresponding
@@ -27,13 +34,6 @@
  of m, for each message.
 */
 
-//#define EXPORT_FRIENDLY 1 /* No crypto! */
-//#define NO_HMAC 1 /* No real hmac */
-
-struct seckey {
-	struct sha256 k;
-};
-
 struct enckey {
 	struct sha256 k;
 };
@@ -74,28 +74,14 @@ static struct hmackey hmackey_from_secret(const unsigned char secret[32])
 }
 
 
-static struct iv iv_from_secret(const unsigned char secret[32], size_t i)
+static void ivs_from_secret(const unsigned char secret[32],
+			    struct iv *iv, struct iv *pad_iv)
 {
-	struct iv iv;
 	struct sha256 sha;
 	sha_with_seed(secret, 2, &sha);
-	memcpy(iv.iv, sha.u.u8, sizeof(iv.iv));
-#ifdef EXPORT_FRIENDLY
-	iv.iv[0] = i*2;
-#endif
-	return iv;
-}
-
-static struct iv pad_iv_from_secret(const unsigned char secret[32], size_t i)
-{
-	struct iv iv;
-	struct sha256 sha;
-	sha_with_seed(secret, 3, &sha);
-	memcpy(iv.iv, sha.u.u8, sizeof(iv.iv));
-#ifdef EXPORT_FRIENDLY
-	iv.iv[0] = i*2 + 1;
-#endif
-	return iv;
+	BUILD_ASSERT(sizeof(*iv) + sizeof(*pad_iv) == sizeof(sha));
+	memcpy(iv->iv, sha.u.u8, sizeof(iv->iv));
+	memcpy(pad_iv->iv, sha.u.u8 + sizeof(iv->iv), sizeof(pad_iv->iv));
 }
 
 /* Not really! */
@@ -108,12 +94,97 @@ static void random_bytes(void *dst, size_t n)
 		d[i] = random() % 256;
 }
 
-static void gen_keys(secp256k1_context *ctx,
-		     struct seckey *seckey, secp256k1_pubkey *pubkey)
+/* Compressed key would start with 0x3?  Subtract from group.  Thanks
+ * Greg Maxwell. */
+static void flip_key(struct seckey *seckey)
+{
+	int i;
+	bool carry = 0;
+
+	const int64_t group[] = {
+		0xFFFFFFFFFFFFFFFFULL,
+		0xFFFFFFFFFFFFFFFEULL,
+		0xBAAEDCE6AF48A03BULL,
+		0xBFD25E8CD0364141ULL
+	};
+
+	for (i = 3; i >= 0; i--) {
+		uint64_t v = be64_to_cpu(seckey->u.be64[i]);
+		if (carry) {
+			/* Beware wrap if v == 0xFFFF.... */
+			carry = (group[i] <= v);
+			v++;
+		} else
+			carry = (group[i] < v);
+
+		v = group[i] - v;
+		seckey->u.be64[i] = cpu_to_be64(v);
+	}
+}
+
+#if 0
+int main(int argc, char *argv[])
+{
+	struct seckey k;
+
+	k.u.be64[0] = cpu_to_be64(0xFFFFFFFFFFFFFFFFULL);
+	k.u.be64[1] = cpu_to_be64(0xFFFFFFFFFFFFFFFEULL);
+	k.u.be64[2] = cpu_to_be64(0xBAAEDCE6AF48A03BULL);
+	k.u.be64[3] = cpu_to_be64(0xBFD25E8CD0364141ULL);
+	flip_key(&k);
+	assert(k.u.be64[0] == 0);
+	assert(k.u.be64[1] == 0);
+	assert(k.u.be64[2] == 0);
+	assert(k.u.be64[3] == 0);
+	flip_key(&k);
+	assert(k.u.be64[0] == cpu_to_be64(0xFFFFFFFFFFFFFFFFULL));
+	assert(k.u.be64[1] == cpu_to_be64(0xFFFFFFFFFFFFFFFEULL));
+	assert(k.u.be64[2] == cpu_to_be64(0xBAAEDCE6AF48A03BULL));
+	assert(k.u.be64[3] == cpu_to_be64(0xBFD25E8CD0364141ULL));
+
+	k.u.be64[0] = cpu_to_be64(0xFFFFFFFFFFFFFFFFULL);
+	k.u.be64[1] = cpu_to_be64(0xFFFFFFFFFFFFFFFEULL);
+	k.u.be64[2] = cpu_to_be64(0xBAAEDCE6AF48A03BULL);
+	k.u.be64[3] = cpu_to_be64(0xBFD25E8CD0364142ULL);
+	flip_key(&k);
+	assert(k.u.be64[0] == 0xFFFFFFFFFFFFFFFFULL);
+	assert(k.u.be64[1] == 0xFFFFFFFFFFFFFFFFULL);
+	assert(k.u.be64[2] == 0xFFFFFFFFFFFFFFFFULL);
+	assert(k.u.be64[3] == 0xFFFFFFFFFFFFFFFFULL);
+	flip_key(&k);
+	assert(k.u.be64[0] == cpu_to_be64(0xFFFFFFFFFFFFFFFFULL));
+	assert(k.u.be64[1] == cpu_to_be64(0xFFFFFFFFFFFFFFFEULL));
+	assert(k.u.be64[2] == cpu_to_be64(0xBAAEDCE6AF48A03BULL));
+	assert(k.u.be64[3] == cpu_to_be64(0xBFD25E8CD0364142ULL));
+
+	return 0;
+}
+#endif
+
+static void random_key(secp256k1_context *ctx,
+		       struct seckey *seckey, secp256k1_pubkey *pkey)
 {
 	do {
-		random_bytes(seckey->k.u.u8, sizeof(seckey->k));
-	} while (!secp256k1_ec_pubkey_create(ctx, pubkey, seckey->k.u.u8));
+		random_bytes(seckey->u.u8, sizeof(seckey->u));
+	} while (!secp256k1_ec_pubkey_create(ctx, pkey, seckey->u.u8));
+}
+
+/* We don't want to spend a byte encoding sign, so make sure it's 0x2 */
+static void gen_keys(secp256k1_context *ctx,
+		     struct seckey *seckey, struct onion_pubkey *pubkey)
+{
+	unsigned char tmp[33];
+	secp256k1_pubkey pkey;
+	size_t len;
+
+	random_key(ctx, seckey, &pkey);
+
+	secp256k1_ec_pubkey_serialize(ctx, tmp, &len, &pkey,
+				      SECP256K1_EC_COMPRESSED);
+	assert(len == sizeof(tmp));
+	if (tmp[0] == 0x3)
+		flip_key(seckey);
+	memcpy(pubkey, tmp+1, sizeof(*pubkey));
 }
 
 /*
@@ -145,33 +216,29 @@ static void gen_keys(secp256k1_context *ctx,
 #define MAX_HOPS 20
 
 struct hop {
-	struct sha256 hmac;
-	/* FIXME: Must use parse/serialize functions. */
-	secp256k1_pubkey pubkey;
 	unsigned char msg[MESSAGE_SIZE];
+	struct onion_pubkey pubkey;
+	struct sha256 hmac;
 };
 
 struct onion {
 	struct hop hop[MAX_HOPS];
 };
 
+/* We peel from the back. */
+static struct hop *myhop(const struct onion *onion)
+{
+	return (struct hop *)&onion->hop[MAX_HOPS-1];
+}
+
 static bool aes_encrypt(void *dst, const void *src, size_t len,
 			const struct enckey *enckey, const struct iv *iv)
 {
-#ifdef EXPORT_FRIENDLY
-	unsigned char *dptr = dst;
-	const unsigned char *sptr = memcheck(src, len);
-	size_t i;
-
-	for (i = 0; i < len; i++)
-		dptr[i] = sptr[i] + iv->iv[0] + i / sizeof(struct hop);
-	return true;
-#else
 	EVP_CIPHER_CTX evpctx;
 	int outlen;
 
 	/* Counter mode allows parallelism in future. */
-	if (EVP_EncryptInit(&evpctx, EVP_aes_256_ctr(),
+	if (EVP_EncryptInit(&evpctx, EVP_aes_128_ctr(),
 			    memcheck(enckey->k.u.u8, sizeof(enckey->k)),
 			    memcheck(iv->iv, sizeof(iv->iv))) != 1)
 		return false;
@@ -187,26 +254,16 @@ static bool aes_encrypt(void *dst, const void *src, size_t len,
 		return false;
 	assert(outlen == 0);
 	return true;
-#endif
 }
 
 static bool aes_decrypt(void *dst, const void *src, size_t len,
 			const struct enckey *enckey, const struct iv *iv)
 {
-#ifdef EXPORT_FRIENDLY
-	unsigned char *dptr = dst;
-	const unsigned char *sptr = memcheck(src, len);
-	size_t i;
-
-	for (i = 0; i < len; i++)
-		dptr[i] = sptr[i] - iv->iv[0] - i / sizeof(struct hop);
-	return true;
-#else
 	EVP_CIPHER_CTX evpctx;
 	int outlen;
 
 	/* Counter mode allows parallelism in future. */
-	if (EVP_DecryptInit(&evpctx, EVP_aes_256_ctr(),
+	if (EVP_DecryptInit(&evpctx, EVP_aes_128_ctr(),
 			    memcheck(enckey->k.u.u8, sizeof(enckey->k)),
 			    memcheck(iv->iv, sizeof(iv->iv))) != 1)
 		return false;
@@ -222,7 +279,6 @@ static bool aes_decrypt(void *dst, const void *src, size_t len,
 		return false;
 	assert(outlen == 0);
 	return true;
-#endif
 }
 
 void dump_contents(const void *data, size_t n)
@@ -237,28 +293,26 @@ void dump_contents(const void *data, size_t n)
 	}
 }
 
-static bool decrypt_padding(struct hop *padding, size_t nhops,
-			    const struct enckey *enckey,
-			    const struct iv *iv)
+static bool aes_encrypt_offset(size_t offset,
+			       void *dst, const void *src, size_t len,
+			       const struct enckey *enckey,
+			       const struct iv *iv)
 {
 	/*
 	 * FIXME: This would be easier if we could set the counter; instead
-	 * we simulate it by decrypting junk before the actual padding.
+	 * we simulate it by encrypting junk before the actual data.
 	 */
-	struct hop tmp[MAX_HOPS];
-
+	char tmp[offset + len];
+	
 	/* Keep valgrind happy. */
-	memset(tmp, 0, (MAX_HOPS - nhops) * sizeof(struct hop));
-
-	memcpy(tmp + MAX_HOPS - nhops, padding, nhops * sizeof(struct hop));
+	memset(tmp, 0, offset);
+	memcpy(tmp + offset, src, len);
 
-	/* FIXME: Assumes we are allowed to decrypt in place! */
-	if (!aes_decrypt((char *)tmp + offsetof(struct hop, msg),
-			 (char *)tmp + offsetof(struct hop, msg),
-			 sizeof(tmp) - offsetof(struct hop, msg), enckey, iv))
+	/* FIXME: Assumes we are allowed to encrypt in place! */
+	if (!aes_encrypt(tmp, tmp, offset+len, enckey, iv))
 		return false;
 
-	memcpy(padding, tmp + MAX_HOPS - nhops, nhops * sizeof(struct hop));
+	memcpy(dst, tmp + offset, len);
 	return true;
 }
 
@@ -277,32 +331,33 @@ static void make_hmac(const struct hop *hops, size_t num_hops,
 		      const struct hmackey *hmackey,
 		      struct sha256 *hmac)
 {
-#ifdef NO_HMAC
-	/* Copy first byte of message on each hop. */
-	size_t i;
-
-	memset(hmac, 0, sizeof(*hmac));
-	for (i = 0; i < MAX_HOPS; i++) {
-		if (i < num_hops)
-			hmac->u.u8[i] = hops[i].msg[0];
-		else
-			hmac->u.u8[i] = padding[i - num_hops].msg[0];
-	}
-#else
 	HMAC_CTX ctx;
 	size_t len, padlen;
 
-	/* Calculate HMAC of pubkey onwards, plus padding. */
+	/* Calculate HMAC of padding then onion up to and including pubkey. */
 	HMAC_CTX_init(&ctx);
 	HMAC_Init_ex(&ctx, memcheck(hmackey->k.u.u8, sizeof(hmackey->k)),
 		     sizeof(hmackey->k), EVP_sha256(), NULL);
-	len = num_hops*sizeof(struct hop) - offsetof(struct hop, pubkey);
-	HMAC_Update(&ctx, memcheck((unsigned char *)hops + offsetof(struct hop, pubkey),
-				   len), len);
 	padlen = (MAX_HOPS - num_hops) * sizeof(struct hop);
 	HMAC_Update(&ctx, memcheck((unsigned char *)padding, padlen), padlen);
+	len = num_hops*sizeof(struct hop) - sizeof(hops->hmac);
+	HMAC_Update(&ctx, memcheck((unsigned char *)hops, len), len);
 	HMAC_Final(&ctx, hmac->u.u8, NULL);
-#endif
+}
+
+void _dump_hex(unsigned char *x, size_t s) {
+	printf(" ");
+	while (s > 0) {
+		printf("%02x", *x);
+		x++; s--;
+	}
+}
+#define dump_hex(x) _dump_hex((void*)&x, sizeof(x))
+void dump_pkey(secp256k1_context *ctx, secp256k1_pubkey pkey) {
+	unsigned char tmp[65];
+	size_t len;
+	secp256k1_ec_pubkey_serialize(ctx, tmp, &len, &pkey, 0);
+	dump_hex(tmp);
 }
 
 static bool check_hmac(struct onion *onion, const struct hmackey *hmackey)
@@ -310,7 +365,7 @@ static bool check_hmac(struct onion *onion, const struct hmackey *hmackey)
 	struct sha256 hmac;
 
 	make_hmac(onion->hop, MAX_HOPS, NULL, hmackey, &hmac);
-	return CRYPTO_memcmp(&hmac, &onion->hop[0].hmac, sizeof(hmac)) == 0;
+	return CRYPTO_memcmp(&hmac, &myhop(onion)->hmac, sizeof(hmac)) == 0;
 }
 
 bool create_onion(const secp256k1_pubkey pubkey[],
@@ -319,37 +374,37 @@ bool create_onion(const secp256k1_pubkey pubkey[],
 		  struct onion *onion)
 {
 	int i;
-	struct seckey *seckeys = tal_arr(NULL, struct seckey, num);
-	secp256k1_pubkey *pubkeys = tal_arr(seckeys, secp256k1_pubkey, num);
-	struct enckey *enckeys = tal_arr(seckeys, struct enckey, num);
-	struct hmackey *hmackeys = tal_arr(seckeys, struct hmackey, num);
-	struct iv *ivs = tal_arr(seckeys, struct iv, num);
-	struct iv *pad_ivs = tal_arr(seckeys, struct iv, num);
-	struct hop **padding = tal_arr(seckeys, struct hop *, num);
-	struct hop **hops = tal_arr(seckeys, struct hop *, num);
+	struct seckey seckeys[MAX_HOPS];
+	struct onion_pubkey pubkeys[MAX_HOPS];
+	struct enckey enckeys[MAX_HOPS];
+	struct hmackey hmackeys[MAX_HOPS];
+	struct iv ivs[MAX_HOPS];
+	struct iv pad_ivs[MAX_HOPS];
+	HMAC_CTX padding_hmac[MAX_HOPS];
+	struct hop padding[MAX_HOPS];
 	size_t junk_hops;
-	secp256k1_context *ctx;
+	secp256k1_context *ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
 	bool ok = false;
 
 	if (num > MAX_HOPS)
 		goto fail;
 
-	ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
-
+	/* FIXME: I think it would be safe to reuse a single disposable key
+	 * here? */
 	/* First generate all the keys. */
 	for (i = 0; i < num; i++) {
 		unsigned char secret[32];
 
 		gen_keys(ctx, &seckeys[i], &pubkeys[i]);
 
+
 		/* Make shared secret. */
-		if (!secp256k1_ecdh(ctx, secret, &pubkey[i], seckeys[i].k.u.u8))
+		if (!secp256k1_ecdh(ctx, secret, &pubkey[i], seckeys[i].u.u8))
 			goto fail;
 
 		hmackeys[i] = hmackey_from_secret(memcheck(secret, 32));
 		enckeys[i] = enckey_from_secret(secret);
-		ivs[i] = iv_from_secret(secret, i);
-		pad_ivs[i] = pad_iv_from_secret(secret, i);
+		ivs_from_secret(secret, &ivs[i], &pad_ivs[i]);
 	}
 
 	/*
@@ -359,18 +414,24 @@ bool create_onion(const secp256k1_pubkey pubkey[],
 	 * and "decrypted" by the others.  So we have to generate that
 	 * forwards.
 	 */
-	for (i = 1; i < num; i++) {
-		/* Each one has 1 padding from previous. */
-		padding[i] = tal_arr(padding, struct hop, i);
-
-		/* Copy padding from previous node. */
-		memcpy(padding[i], padding[i-1], sizeof(struct hop)*(i-1));
-		/* Previous node "decrypts" it before handing to us */
-		if (!decrypt_padding(padding[i], i-1,
-				     &enckeys[i-1], &ivs[i-1]))
-			goto fail;
-		/* And generates another lot of padding. */
-		add_padding(padding[i]+i-1, &enckeys[i-1], &pad_ivs[i-1]);
+	for (i = 0; i < num; i++) {
+		if (i > 0) {
+			/* Previous node decrypts padding before passing on. */
+			aes_decrypt(padding, padding, sizeof(struct hop)*(i-1),
+				    &enckeys[i-1], &ivs[i-1]);
+			memmove(padding + 1, padding,
+				sizeof(struct hop)*(i-1));
+		}
+		/* And generates more padding for next node. */
+		add_padding(&padding[0], &enckeys[i-1], &pad_ivs[i-1]);
+		HMAC_CTX_init(&padding_hmac[i]);
+		HMAC_Init_ex(&padding_hmac[i],
+			     hmackeys[i].k.u.u8, sizeof(hmackeys[i].k),
+			     EVP_sha256(), NULL);
+		HMAC_Update(&padding_hmac[i],
+			    memcheck((unsigned char *)padding,
+				     i * sizeof(struct hop)),
+			    i * sizeof(struct hop));
 	}
 
 	/*
@@ -380,77 +441,83 @@ bool create_onion(const secp256k1_pubkey pubkey[],
 	/* Unused hops filled with random, so even recipient can't tell
 	 * how many were used. */
 	junk_hops = MAX_HOPS - num;
+	random_bytes(onion->hop, junk_hops * sizeof(struct hop));
 
 	for (i = num - 1; i >= 0; i--) {
-		size_t other_hops;
-		struct hop *myonion;
+		size_t other_hops, len;
+		struct hop *myhop;
 
 		other_hops = num - i - 1 + junk_hops;
-		myonion = hops[i] = tal_arr(hops, struct hop, 1 + other_hops);
-		if (i == num - 1) {
-			/* Fill with junk. */
-			random_bytes(myonion + 1,
-				     other_hops * sizeof(struct hop));
-		} else {
-			/* Copy from next hop. */
-			memcpy(myonion + 1, hops[i+1],
-			       other_hops * sizeof(struct hop));
-		}
+
+		/* Our entry is at tail of onion. */
+		myhop = onion->hop + other_hops;
 
 		/* Now populate our hop. */
-		myonion->pubkey = pubkeys[i];
+		myhop->pubkey = pubkeys[i];
 		/* Set message. */
 		assert(strlen(msg[i]) < MESSAGE_SIZE);
-		memset(myonion->msg, 0, MESSAGE_SIZE);
-		strcpy((char *)myonion->msg, msg[i]);
-
-		/* Encrypt whole thing from message onwards. */
-		if (!aes_encrypt(&myonion->msg, &myonion->msg,
-				 (1 + other_hops) * sizeof(struct hop)
-				 - offsetof(struct hop, msg),
-				 &enckeys[i], &ivs[i]))
+		memset(myhop->msg, 0, MESSAGE_SIZE);
+		strcpy((char *)myhop->msg, msg[i]);
+
+		/* Encrypt whole thing, including our message, but we
+		 * aware it will be offset by the prepended padding. */
+		if (!aes_encrypt_offset(i * sizeof(struct hop),
+					onion, onion,
+					other_hops * sizeof(struct hop)
+					+ sizeof(myhop->msg),
+					&enckeys[i], &ivs[i]))
 			goto fail;
 
 		/* HMAC covers entire thing except hmac itself. */
-		make_hmac(myonion, 1 + other_hops, padding[i],
-			  &hmackeys[i], &myonion->hmac);
+		len = (other_hops + 1)*sizeof(struct hop) - sizeof(myhop->hmac);
+		HMAC_Update(&padding_hmac[i],
+			    memcheck((unsigned char *)onion, len), len);
+		HMAC_Final(&padding_hmac[i], myhop->hmac.u.u8, NULL);
 	}
 
-	/* Transfer results to onion, for first node. */
-	assert(tal_count(hops[0]) == MAX_HOPS);
-	memcpy(onion->hop, hops[0], sizeof(onion->hop));
 	ok = true;
-
 fail:
-	tal_free(seckeys);
 	secp256k1_context_destroy(ctx);
 	return ok;
 }
 
+static bool pubkey_parse(const secp256k1_context *ctx,
+			 secp256k1_pubkey* pubkey,
+			 struct onion_pubkey *pkey)
+{
+	unsigned char tmp[33];
+
+	tmp[0] = 0x2;
+	memcpy(tmp+1, pkey, sizeof(*pkey));
+	return secp256k1_ec_pubkey_parse(ctx, pubkey, tmp, sizeof(tmp));
+}
+
 /*
  * Decrypt onion, return true if onion->hop[0] is valid.
  *
  * Returns enckey and pad_iv for use in unwrap.
  */
 bool decrypt_onion(const struct seckey *myseckey, struct onion *onion,
-		   struct enckey *enckey, struct iv *pad_iv, size_t i)
+		   struct enckey *enckey, struct iv *pad_iv)
 {
 	secp256k1_context *ctx;
 	unsigned char secret[32];
 	struct hmackey hmackey;
 	struct iv iv;
+	secp256k1_pubkey pubkey;
 
 	ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
 
+	if (!pubkey_parse(ctx, &pubkey, &myhop(onion)->pubkey))
+		goto fail;
+	
 	/* Extract shared secret. */
-	if (!secp256k1_ecdh(ctx, secret, &onion->hop[0].pubkey,
-			    myseckey->k.u.u8))
+	if (!secp256k1_ecdh(ctx, secret, &pubkey, myseckey->u.u8))
 		goto fail;
 
 	hmackey = hmackey_from_secret(secret);
 	*enckey = enckey_from_secret(secret);
-	iv = iv_from_secret(secret, i);
-	*pad_iv = pad_iv_from_secret(secret, i);
+	ivs_from_secret(secret, &iv, pad_iv);
 
 	/* Check HMAC. */
 #if 0
@@ -478,9 +545,11 @@ bool decrypt_onion(const struct seckey *myseckey, struct onion *onion,
 	if (!check_hmac(onion, &hmackey))
 		goto fail;
 
-	/* Decrypt everything after pubkey. */
-	if (!aes_decrypt(onion->hop[0].msg, onion->hop[0].msg,
-			 sizeof(*onion) - offsetof(struct hop, msg),
+	/* Decrypt everything up to pubkey. */
+	/* FIXME: Assumes we can decrypt in place! */
+	if (!aes_decrypt(onion, onion,
+			 sizeof(struct hop) * (MAX_HOPS-1)
+			 + sizeof(myhop(onion)->msg),
 			 enckey, &iv))
 		goto fail;
 	
@@ -496,55 +565,117 @@ fail:
 bool peel_onion(struct onion *onion,
 		const struct enckey *enckey, const struct iv *pad_iv)
 {
-	/* Move next one to front. */
-	memmove(&onion->hop[0], &onion->hop[1],
+	/* Move next one to back. */
+	memmove(&onion->hop[1], &onion->hop[0],
 		sizeof(*onion) - sizeof(onion->hop[0]));
 
 	/* Add random-looking (but predictable) padding. */
-	memset(&onion->hop[MAX_HOPS-1], 0, sizeof(onion->hop[MAX_HOPS-1]));
-	return aes_encrypt(&onion->hop[MAX_HOPS-1], &onion->hop[MAX_HOPS-1],
-			   sizeof(onion->hop[MAX_HOPS-1]), enckey, pad_iv);
+	memset(&onion->hop[0], 0, sizeof(onion->hop[0]));
+	return aes_encrypt(&onion->hop[0], &onion->hop[0],
+			   sizeof(onion->hop[0]), enckey, pad_iv);
+}
+
+static bool parse_onion_pubkey(secp256k1_context *ctx,
+			       const char *arg, secp256k1_pubkey *pubkey)
+{
+	unsigned char tmp[33] = { };
+
+	if (!hex_decode(arg, strlen(arg), tmp, sizeof(tmp)))
+		return false;
+
+	return secp256k1_ec_pubkey_parse(ctx, pubkey, tmp, sizeof(tmp));
+}
+
+static char *make_message(secp256k1_context *ctx,
+		const secp256k1_pubkey *pubkey)
+{
+	char *m;
+	unsigned char tmp[33];
+	size_t len;
+	char hexstr[hex_str_size(20)];
+
+	secp256k1_ec_pubkey_serialize(ctx, tmp, &len, pubkey,
+				      SECP256K1_EC_COMPRESSED);
+	hex_encode(tmp+1, 20, hexstr, sizeof(hexstr));
+	asprintf(&m, "Message for %s...", hexstr);
+	return m;
 }
 
 int main(int argc, char *argv[])
 {
 	secp256k1_context *ctx;
-	size_t i, hops;
-	struct seckey seckeys[MAX_HOPS];
-	secp256k1_pubkey pubkeys[MAX_HOPS];
-	char *msgs[MAX_HOPS];
 	struct onion onion;
+	bool generate = false, decode = false;
 
-	assert(EVP_CIPHER_iv_length(EVP_aes_256_ctr()) == sizeof(struct iv));
-	
-	if (argc != 2)
-		errx(1, "Usage: %s <num hops>", argv[0]);
-	hops = atoi(argv[1]);
-	if (hops == 0 || hops > MAX_HOPS)
-		errx(1, "%s is invalid number of hops", argv[1]);
+	assert(EVP_CIPHER_iv_length(EVP_aes_128_ctr()) == sizeof(struct iv));
 	
-	ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
-	for (i = 0; i < hops; i++) {
-		asprintf(&msgs[i], "Message to %zu", i);
-		gen_keys(ctx, &seckeys[i], &pubkeys[i]);
-	}
+	opt_register_noarg("--help|-h", opt_usage_and_exit,
+			   "--generate <pubkey>... OR\n"
+			   "--decode <privkey>\n"
+			   "Either create an onion message, or decode one step",
+			   "Print this message.");
+	opt_register_noarg("--generate",
+			   opt_set_bool, &generate,
+			   "Generate onion through the given hex pubkeys");
+	opt_register_noarg("--decode",
+			   opt_set_bool, &decode,
+			   "Decode onion given the private key");
+	opt_register_version();
+
+ 	opt_parse(&argc, argv, opt_log_stderr_exit);
 
-	if (!create_onion(pubkeys, msgs, hops, &onion))
-		errx(1, "Creating onion packet failed");
+	ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
+	if (generate) {
+		secp256k1_pubkey pubkeys[MAX_HOPS];
+		char *msgs[MAX_HOPS];
+		size_t i;
+
+		if (argc == 1)
+			opt_usage_exit_fail("Expected at least one pubkey");
+		if (argc-1 > MAX_HOPS)
+			opt_usage_exit_fail("Expected at most %u pubkeys",
+					    MAX_HOPS);
+		for (i = 1; i < argc; i++) {
+			if (!parse_onion_pubkey(ctx, argv[i], &pubkeys[i-1]))
+				errx(1, "Bad pubkey '%s'", argv[i]);
+			msgs[i-1] = make_message(ctx, &pubkeys[i-1]);
+		}
 
-	/* Now parse and peel. */
-	for (i = 0; i < hops; i++) {
+		if (!create_onion(pubkeys, msgs, argc - 1, &onion))
+			errx(1, "Creating onion packet failed");
+		if (!write_all(STDOUT_FILENO, &onion, sizeof(onion)))
+			err(1, "Writing onion packet");
+		return 0;
+	} else if (decode) {
+		struct seckey seckey;
+		secp256k1_pubkey pubkey;
 		struct enckey enckey;
 		struct iv pad_iv;
 
-		printf("Decrypting with key %zi\n", i);
-		if (!decrypt_onion(&seckeys[i], &onion, &enckey, &pad_iv, i))
-			errx(1, "Decrypting onion for hop %zi", i);
-		if (strcmp((char *)onion.hop[0].msg, msgs[i]) != 0)
-			errx(1, "Bad message for hop %zi", i);
+		if (argc != 2)
+			opt_usage_exit_fail("Expect a privkey with --decode");
+
+		if (!hex_decode(argv[1], strlen(argv[1]), &seckey, sizeof(seckey)))
+			errx(1, "Invalid private key hex '%s'", argv[1]);
+		if (!secp256k1_ec_pubkey_create(ctx, &pubkey, seckey.u.u8))
+			errx(1, "Invalid private key '%s'", argv[1]);
+
+		if (!read_all(STDIN_FILENO, &onion, sizeof(onion)))
+			errx(1, "Reading in onion");
+
+		if (!decrypt_onion(&seckey, &onion, &enckey, &pad_iv))
+			errx(1, "Failed decrypting onion for '%s'", argv[1]);
+		if (strncmp((char *)myhop(&onion)->msg, make_message(ctx, &pubkey),
+			    sizeof(myhop(&onion)->msg)))
+			errx(1, "Bad message '%s'", (char *)myhop(&onion)->msg);
 		if (!peel_onion(&onion, &enckey, &pad_iv))
-			errx(1, "Peeling onion for hop %zi", i);
-	}
+			errx(1, "Peeling onion for '%s'", argv[1]);
+		if (!write_all(STDOUT_FILENO, &onion, sizeof(onion)))
+			err(1, "Writing onion packet");
+		return 0;
+	} else
+		opt_usage_exit_fail("Need --decode or --generate");
+		
 	secp256k1_context_destroy(ctx);
 	return 0;
 }

test/test_onion.py

@@ -0,0 +1,345 @@
+#!/usr/bin/env python
+
+import argparse
+import sys
+import time
+
+from hashlib import sha256
+from binascii import hexlify, unhexlify
+import hmac
+import random
+
+from cryptography.hazmat.primitives.ciphers import Cipher, modes, algorithms
+from cryptography.hazmat.primitives.ciphers.algorithms import AES
+from cryptography.hazmat.primitives.ciphers.modes import CTR
+from cryptography.hazmat.backends import default_backend
+# http://cryptography.io
+
+from pyelliptic import ecc
+
+class MyEx(Exception): pass
+
+def hmac_sha256(k, m):
+    return hmac.new(k, m, sha256).digest()
+
+
+
+
+
+
+## pyelliptic doesn't support compressed pubkey representations
+## so we have to add some code...
+from pyelliptic.openssl import OpenSSL
+import ctypes
+
+OpenSSL.EC_POINT_set_compressed_coordinates_GFp = \
+        OpenSSL._lib.EC_POINT_set_compressed_coordinates_GFp
+OpenSSL.EC_POINT_set_compressed_coordinates_GFp.restype = ctypes.c_int
+OpenSSL.EC_POINT_set_compressed_coordinates_GFp.argtypes = [
+    ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p, ctypes.c_int,
+    ctypes.c_void_p]
+
+def ecc_ecdh_key(sec, pub):
+    assert isinstance(sec, ecc.ECC)
+    if isinstance(pub, ecc.ECC):
+        pub = pub.get_pubkey()
+    #return sec.get_ecdh_key(pub)
+
+    pubkey_x, pubkey_y = ecc.ECC._decode_pubkey(pub, 'binary')
+
+    other_key = other_pub_key_x = other_pub_key_y = other_pub_key = None
+    own_priv_key = res = res_x = res_y = None
+    try:
+            other_key = OpenSSL.EC_KEY_new_by_curve_name(sec.curve)
+            if other_key == 0:
+                raise Exception("[OpenSSL] EC_KEY_new_by_curve_name FAIL ... " + OpenSSL.get_error())
+
+            other_pub_key_x = OpenSSL.BN_bin2bn(pubkey_x, len(pubkey_x), 0)
+            other_pub_key_y = OpenSSL.BN_bin2bn(pubkey_y, len(pubkey_y), 0)
+
+            other_group = OpenSSL.EC_KEY_get0_group(other_key)
+            other_pub_key = OpenSSL.EC_POINT_new(other_group)
+            if (other_pub_key == None):
+                raise Exception("[OpenSSl] EC_POINT_new FAIL ... " + OpenSSL.get_error())
+
+            if (OpenSSL.EC_POINT_set_affine_coordinates_GFp(other_group,
+                                                            other_pub_key,
+                                                            other_pub_key_x,
+                                                            other_pub_key_y,
+                                                            0)) == 0:
+                raise Exception(
+                    "[OpenSSL] EC_POINT_set_affine_coordinates_GFp FAIL ..." + OpenSSL.get_error())
+
+            own_priv_key = OpenSSL.BN_bin2bn(sec.privkey, len(sec.privkey), 0)
+
+            res = OpenSSL.EC_POINT_new(other_group)
+            if (OpenSSL.EC_POINT_mul(other_group, res, 0, other_pub_key, own_priv_key, 0)) == 0:
+                raise Exception(
+                    "[OpenSSL] EC_POINT_mul FAIL ..." + OpenSSL.get_error())
+
+            res_x = OpenSSL.BN_new()
+            res_y = OpenSSL.BN_new()
+
+            if (OpenSSL.EC_POINT_get_affine_coordinates_GFp(other_group, res,
+                                                            res_x,
+                                                            res_y, 0
+                                                            )) == 0:
+                raise Exception(
+                    "[OpenSSL] EC_POINT_get_affine_coordinates_GFp FAIL ... " + OpenSSL.get_error())
+
+            resx = OpenSSL.malloc(0, OpenSSL.BN_num_bytes(res_x))
+            resy = OpenSSL.malloc(0, OpenSSL.BN_num_bytes(res_y))
+
+            OpenSSL.BN_bn2bin(res_x, resx)
+            resx = resx.raw
+            OpenSSL.BN_bn2bin(res_y, resy)
+            resy = resy.raw
+
+            return resx, resy
+
+    finally:
+            if other_key: OpenSSL.EC_KEY_free(other_key)
+            if other_pub_key_x: OpenSSL.BN_free(other_pub_key_x)
+            if other_pub_key_y: OpenSSL.BN_free(other_pub_key_y)
+            if other_pub_key: OpenSSL.EC_POINT_free(other_pub_key)
+            if own_priv_key: OpenSSL.BN_free(own_priv_key)
+            if res: OpenSSL.EC_POINT_free(res)
+            if res_x: OpenSSL.BN_free(res_x)
+            if res_y: OpenSSL.BN_free(res_y)
+
+def get_pos_y_for_x(pubkey_x, yneg=0):
+    key = pub_key = pub_key_x = pub_key_y = None
+    try:
+        key = OpenSSL.EC_KEY_new_by_curve_name(OpenSSL.get_curve('secp256k1'))
+        group = OpenSSL.EC_KEY_get0_group(key)
+        pub_key_x = OpenSSL.BN_bin2bn(pubkey_x, len(pubkey_x), 0)
+        pub_key = OpenSSL.EC_POINT_new(group)
+
+        if OpenSSL.EC_POINT_set_compressed_coordinates_GFp(group, pub_key,
+                                                           pub_key_x, yneg, 0) == 0:
+            raise Exception("[OpenSSL] EC_POINT_set_compressed_coordinates_GFp FAIL ... " + OpenSSL.get_error())
+
+
+        pub_key_y = OpenSSL.BN_new()
+        if (OpenSSL.EC_POINT_get_affine_coordinates_GFp(group, pub_key,
+                                                        pub_key_x,
+                                                        pub_key_y, 0
+                                                       )) == 0:
+            raise Exception("[OpenSSL] EC_POINT_get_affine_coordinates_GFp FAIL ... " + OpenSSL.get_error())
+
+        pubkeyy = OpenSSL.malloc(0, OpenSSL.BN_num_bytes(pub_key_y))
+        OpenSSL.BN_bn2bin(pub_key_y, pubkeyy)
+        pubkeyy = pubkeyy.raw
+        field_size = OpenSSL.EC_GROUP_get_degree(OpenSSL.EC_KEY_get0_group(key))
+        secret_len = int((field_size + 7) / 8)
+        if len(pubkeyy) < secret_len:
+            pubkeyy = pubkeyy.rjust(secret_len, b'\0')
+        return pubkeyy
+    finally:
+        if key is not None: OpenSSL.EC_KEY_free(key)
+        if pub_key is not None: OpenSSL.EC_POINT_free(pub_key)
+        if pub_key_x is not None: OpenSSL.BN_free(pub_key_x)
+        if pub_key_y is not None: OpenSSL.BN_free(pub_key_y)
+
+def ec_decompress(pubkey, curve='secp256k1'):
+    if pubkey[0] == '\x02' or pubkey[0] == '\x03':
+        yneg = ord(pubkey[0]) & 1
+        pubkey = "\x04" + pubkey[1:] + get_pos_y_for_x(pubkey[1:], yneg=yneg)
+    elif pubkey[0] == '\x04':
+        pass
+    else:
+        raise Exception("Unrecognised pubkey format: %s" % (pubkey,))
+    return pubkey
+
+class Onion(object):
+    HMAC_LEN = 32
+    PKEY_LEN = 32
+    MSG_LEN = 128
+    ZEROES = b"\x00" * (HMAC_LEN + PKEY_LEN + MSG_LEN)
+
+    @staticmethod
+    def tweak_sha(sha, d):
+        sha = sha.copy()
+        sha.update(d)
+        return sha.digest()
+
+    @classmethod
+    def get_ecdh_secrets(cls, sec, pkey_x, pkey_y):
+        pkey = unhexlify('04') + pkey_x + pkey_y
+        tmp_key = ecc.ECC(curve='secp256k1', pubkey=pkey)
+        sec_x, sec_y = ecc_ecdh_key(sec, tmp_key)
+
+        b = '\x02' if ord(sec_y[-1]) % 2 == 0 else '\x03'
+        sec = sha256(sha256(b + sec_x).digest())
+
+        enckey = cls.tweak_sha(sec, b'\x00')[:16]
+        hmac   = cls.tweak_sha(sec, b'\x01')
+        ivs    = cls.tweak_sha(sec, b'\x02')
+        iv, pad_iv = ivs[:16], ivs[16:]
+
+        return enckey, hmac, iv, pad_iv
+
+    def enc_pad(self, enckey, pad_iv):
+        aes = Cipher(AES(enckey), CTR(pad_iv),
+                     default_backend()).encryptor()
+        return aes.update(self.ZEROES)
+
+class OnionDecrypt(Onion):
+    def __init__(self, onion, my_ecc):
+        self.my_ecc = my_ecc
+
+        hmac_end = len(onion)
+        pkey_end = hmac_end - self.HMAC_LEN
+        self.msg_end = pkey_end - self.PKEY_LEN
+        self.fwd_end = self.msg_end - self.MSG_LEN
+
+        self.onion = onion
+        self.pkey = onion[self.msg_end:pkey_end]
+        self.hmac = onion[pkey_end:hmac_end]
+
+        self.get_secrets()
+
+    def decrypt(self):
+        pad = self.enc_pad(self.enckey, self.pad_iv)
+
+        aes = Cipher(AES(self.enckey), CTR(self.iv),
+                     default_backend()).decryptor()
+        self.fwd = pad + aes.update(self.onion[:self.fwd_end])
+        self.msg = aes.update(self.onion[self.fwd_end:self.msg_end])
+
+    def get_secrets(self):
+        pkey_x = self.pkey
+        pkey_y = get_pos_y_for_x(pkey_x) # always positive by design
+        enckey, hmac, iv, pad_iv = self.get_ecdh_secrets(self.my_ecc, pkey_x, pkey_y)
+        if not self.check_hmac(hmac):
+            raise Exception("HMAC did not verify")
+        self.enckey = enckey
+        self.iv     = iv
+        self.pad_iv = pad_iv
+
+    def check_hmac(self, hmac_key):
+        calc = hmac_sha256(hmac_key, self.onion[:-self.HMAC_LEN])
+        return calc == self.hmac
+
+class OnionEncrypt(Onion):
+    def __init__(self, msgs, pubkeys):
+        assert len(msgs) == len(pubkeys)
+        assert 0 < len(msgs) <= 20
+        assert all( len(m) <= self.MSG_LEN for m in msgs )
+
+        msgs = [m + "\0"*(self.MSG_LEN - len(m)) for m in msgs]
+        pubkeys = [ecc.ECC(pubkey=pk, curve='secp256k1') for pk in pubkeys]
+        n = len(msgs)
+
+        tmpkeys = []
+        tmppubkeys = []
+        for i in range(n):
+            while True:
+                t = ecc.ECC(curve='secp256k1')
+                if ord(t.pubkey_y[-1]) % 2 == 0:
+                    break
+                # or do the math to "flip" the secret key and pub key
+            tmpkeys.append(t)
+            tmppubkeys.append(t.pubkey_x)
+
+        enckeys, hmacs, ivs, pad_ivs = zip(*[self.get_ecdh_secrets(tmpkey, pkey.pubkey_x, pkey.pubkey_y)
+            for tmpkey, pkey in zip(tmpkeys, pubkeys)])
+
+        # padding takes the form:
+        #  E_(n-1)(0000s)
+        #  D_(n-1)(
+        #      E(n-2)(0000s)
+        #      D(n-2)(
+        #          ...
+        #      )
+        #  )
+
+        padding = ""
+        for i in range(n-1):
+             pad = self.enc_pad(enckeys[i], pad_ivs[i])
+             aes = Cipher(AES(enckeys[i]), CTR(ivs[i]),
+                     default_backend()).decryptor()
+             padding = pad + aes.update(padding)
+
+        if n < 20:
+            padding += str(bytearray(random.getrandbits(8)
+                             for _ in range(len(self.ZEROES) * (20-n))))
+
+        # to encrypt the message we need to bump the counter past all
+        # the padding, then just encrypt the final message
+        aes = Cipher(AES(enckeys[-1]), CTR(ivs[-1]),
+            default_backend()).encryptor()
+        aes.update(padding) # don't care about cyphertext
+        msgenc = aes.update(msgs[-1])
+
+        msgenc = padding + msgenc + tmppubkeys[-1]
+        del padding
+        msgenc += hmac_sha256(hmacs[-1], msgenc)
+
+        # *PHEW*
+        # now iterate
+
+        for i in reversed(range(n-1)):
+            # drop the padding this node will add
+            msgenc = msgenc[len(self.ZEROES):]
+            # adding the msg
+            msgenc += msgs[i]
+            # encrypt it
+            aes = Cipher(AES(enckeys[i]), CTR(ivs[i]),
+                default_backend()).encryptor()
+            msgenc = aes.update(msgenc)
+            # add the tmp key
+            msgenc += tmppubkeys[i]
+            # add the hmac
+            msgenc += hmac_sha256(hmacs[i], msgenc)
+        self.onion = msgenc
+
+def generate(args):
+    server_keys = []
+    msgs = []
+    for k in args.pubkeys:
+        k = unhexlify(k)
+        msgs.append("Message for %s..." % (hexlify(k[1:21]),))
+        k = ec_decompress(k)
+        server_keys.append(k)
+    o = OnionEncrypt(msgs, server_keys)
+    sys.stdout.write(o.onion)
+    return
+
+def decode(args):
+    msg = sys.stdin.read()
+    key = ecc.ECC(privkey=unhexlify(args.seckey),
+                  pubkey=ec_decompress(unhexlify(args.pubkey)),
+                  curve='secp256k1')
+    o = OnionDecrypt(msg, key)
+    o.decrypt()
+    #sys.stderr.write("Message: \"%s\"\n" % (o.msg,))
+    want_msg = "Message for %s..." % (args.pubkey[2:42])
+    if o.msg != want_msg + "\0"*(Onion.MSG_LEN - len(want_msg)):
+        raise Exception("Unexpected message: \"%s\" (wanted: %s)" % (o.msg, want_msg))
+
+    sys.stdout.write(o.fwd)
+
+def main(argv):
+    parser = argparse.ArgumentParser(description="Process some integers.")
+    sp = parser.add_subparsers()
+    p = sp.add_parser("generate")
+    p.add_argument("pubkeys", nargs='+', help="public keys of recipients")
+    p.set_defaults(func=generate)
+
+    p = sp.add_parser("decode")
+    p.add_argument("seckey", help="secret key for router")
+    p.add_argument("pubkey", help="public key for router")
+    p.set_defaults(func=decode)
+
+    args = parser.parse_args(argv)
+
+    return args.func(args)
+
+
+
+
+if __name__ == "__main__":
+    main(sys.argv[1:])
+    sys.exit(0)
+