Slightly simplify method/cipher/MAC definitions

6 files changed, 75 insertions, 153 deletions

diff --git a/src/methods/cipher_test/cipher_test.c b/src/methods/cipher_test/cipher_test.c
index 9f0b600..050e2a5 100644
--- a/src/methods/cipher_test/cipher_test.c
+++ b/src/methods/cipher_test/cipher_test.c
@@ -34,7 +34,6 @@ struct fastd_method_session_state {
 	const fastd_cipher_t *cipher;
 	const fastd_cipher_context_t *cipher_ctx;
 	fastd_cipher_state_t *cipher_state;
-	size_t ivlen;
 };
 
 
@@ -70,22 +69,13 @@ static size_t method_max_packet_size(fastd_context_t *ctx) {
 }
 
 
-static size_t method_min_head_space(fastd_context_t *ctx UNUSED) {
-	return 0;
-}
-
-static size_t method_min_tail_space(fastd_context_t *ctx UNUSED) {
-	return (sizeof(fastd_block128_t)-1);
-}
-
-
 static size_t method_key_length(fastd_context_t *ctx, const char *name) {
 	const fastd_cipher_t *cipher = NULL;
 	const fastd_cipher_context_t *cctx;
 	if (!cipher_get(ctx, name, &cipher, &cctx))
 		exit_bug(ctx, "cipher-test: can't get cipher key length");
 
-	return cipher->key_length(ctx, cctx);
+	return cipher->key_length;
 }
 
 static fastd_method_session_state_t* method_session_init(fastd_context_t *ctx, const char *name, const uint8_t *secret, bool initiator) {
@@ -97,7 +87,6 @@ static fastd_method_session_state_t* method_session_init(fastd_context_t *ctx, c
 		exit_bug(ctx, "cipher-test: can't instanciate cipher");
 
 	session->cipher_state = session->cipher->init_state(ctx, session->cipher_ctx, secret);
-	session->ivlen = session->cipher->iv_length(ctx, session->cipher_state);
 
 	pr_warn(ctx, "using cipher-test method; this method must be used for testing and benchmarks only");
 
@@ -134,11 +123,11 @@ static bool method_encrypt(fastd_context_t *ctx, fastd_peer_t *peer UNUSED, fast
 	if (tail_len)
 		memset(in.data+in.len, 0, tail_len);
 
-	uint8_t nonce[session->ivlen];
-	if (session->ivlen) {
-		memset(nonce, 0, session->ivlen);
-		memcpy(nonce, session->common.send_nonce, min_size_t(COMMON_NONCEBYTES, session->ivlen));
-		nonce[session->ivlen-1] = 1;
+	uint8_t nonce[session->cipher->iv_length];
+	if (session->cipher->iv_length) {
+		memset(nonce, 0, session->cipher->iv_length);
+		memcpy(nonce, session->common.send_nonce, min_size_t(COMMON_NONCEBYTES, session->cipher->iv_length));
+		nonce[session->cipher->iv_length-1] = 1;
 	}
 
 	int n_blocks = block_count(in.len, sizeof(fastd_block128_t));
@@ -177,11 +166,11 @@ static bool method_decrypt(fastd_context_t *ctx, fastd_peer_t *peer, fastd_metho
 	if (common_nonce[COMMON_NONCEBYTES]) /* flags */
 		return false;
 
-	uint8_t nonce[session->ivlen];
-	if (session->ivlen) {
-		memset(nonce, 0, session->ivlen);
-		memcpy(nonce, common_nonce, min_size_t(COMMON_NONCEBYTES, session->ivlen));
-		nonce[session->ivlen-1] = 1;
+	uint8_t nonce[session->cipher->iv_length];
+	if (session->cipher->iv_length) {
+		memset(nonce, 0, session->cipher->iv_length);
+		memcpy(nonce, common_nonce, min_size_t(COMMON_NONCEBYTES, session->cipher->iv_length));
+		nonce[session->cipher->iv_length-1] = 1;
 	}
 
 	int64_t age;
@@ -219,10 +208,10 @@ const fastd_method_t fastd_method_cipher_test = {
 	.provides = method_provides,
 
 	.max_packet_size = method_max_packet_size,
-	.min_encrypt_head_space = method_min_head_space,
-	.min_decrypt_head_space = method_min_head_space,
-	.min_encrypt_tail_space = method_min_tail_space,
-	.min_decrypt_tail_space = method_min_tail_space,
+	.min_encrypt_head_space = 0,
+	.min_decrypt_head_space = 0,
+	.min_encrypt_tail_space = sizeof(fastd_block128_t)-1,
+	.min_decrypt_tail_space = sizeof(fastd_block128_t)-1,
 
 	.key_length = method_key_length,
 	.session_init = method_session_init,
diff --git a/src/methods/generic_gcm/generic_gcm.c b/src/methods/generic_gcm/generic_gcm.c
index 9c31ec4..a35a6c9 100644
--- a/src/methods/generic_gcm/generic_gcm.c
+++ b/src/methods/generic_gcm/generic_gcm.c
@@ -34,7 +34,6 @@ struct fastd_method_session_state {
 	const fastd_cipher_t *cipher;
 	const fastd_cipher_context_t *cipher_ctx;
 	fastd_cipher_state_t *cipher_state;
-	size_t ivlen;
 
 	const fastd_mac_t *ghash;
 	const fastd_mac_context_t *ghash_ctx;
@@ -77,30 +76,13 @@ static size_t method_max_packet_size(fastd_context_t *ctx) {
 }
 
 
-static size_t method_min_encrypt_head_space(fastd_context_t *ctx UNUSED) {
-	return sizeof(fastd_block128_t);
-}
-
-static size_t method_min_decrypt_head_space(fastd_context_t *ctx UNUSED) {
-	return 0;
-}
-
-static size_t method_min_encrypt_tail_space(fastd_context_t *ctx UNUSED) {
-	return (sizeof(fastd_block128_t)-1);
-}
-
-static size_t method_min_decrypt_tail_space(fastd_context_t *ctx UNUSED) {
-	return (2*sizeof(fastd_block128_t)-1);
-}
-
-
 static size_t method_key_length(fastd_context_t *ctx, const char *name) {
 	const fastd_cipher_t *cipher = NULL;
 	const fastd_cipher_context_t *cctx;
 	if (!cipher_get(ctx, name, &cipher, &cctx))
 		exit_bug(ctx, "generic-gcm: can't get cipher key length");
 
-	return cipher->key_length(ctx, cctx);
+	return cipher->key_length;
 }
 
 static fastd_method_session_state_t* method_session_init(fastd_context_t *ctx, const char *name, const uint8_t *secret, bool initiator) {
@@ -116,12 +98,11 @@ static fastd_method_session_state_t* method_session_init(fastd_context_t *ctx, c
 	static const fastd_block128_t zeroblock = {};
 	fastd_block128_t H;
 
-	session->ivlen = session->cipher->iv_length(ctx, session->cipher_state);
-	if (session->ivlen <= COMMON_NONCEBYTES)
+	if (session->cipher->iv_length <= COMMON_NONCEBYTES)
 		exit_bug(ctx, "generic-gcm: iv_length to small");
 
-	uint8_t zeroiv[session->ivlen];
-	memset(zeroiv, 0, session->ivlen);
+	uint8_t zeroiv[session->cipher->iv_length];
+	memset(zeroiv, 0, session->cipher->iv_length);
 
 	session->cipher->crypt(ctx, session->cipher_state, &H, &zeroblock, sizeof(fastd_block128_t), zeroiv);
 
@@ -185,10 +166,10 @@ static bool method_encrypt(fastd_context_t *ctx, fastd_peer_t *peer UNUSED, fast
 	if (tail_len)
 		memset(in.data+in.len, 0, tail_len);
 
-	uint8_t nonce[session->ivlen];
-	memset(nonce, 0, session->ivlen);
+	uint8_t nonce[session->cipher->iv_length];
+	memset(nonce, 0, session->cipher->iv_length);
 	memcpy(nonce, session->common.send_nonce, COMMON_NONCEBYTES);
-	nonce[session->ivlen-1] = 1;
+	nonce[session->cipher->iv_length-1] = 1;
 
 	int n_blocks = block_count(in.len, sizeof(fastd_block128_t));
 
@@ -238,10 +219,10 @@ static bool method_decrypt(fastd_context_t *ctx, fastd_peer_t *peer, fastd_metho
 	if (((const uint8_t*)in.data)[COMMON_NONCEBYTES]) /* flags */
 		return false;
 
-	uint8_t nonce[session->ivlen];
-	memset(nonce, 0, session->ivlen);
+	uint8_t nonce[session->cipher->iv_length];
+	memset(nonce, 0, session->cipher->iv_length);
 	memcpy(nonce, in.data, COMMON_NONCEBYTES);
-	nonce[session->ivlen-1] = 1;
+	nonce[session->cipher->iv_length-1] = 1;
 
 	int64_t age;
 	if (!fastd_method_is_nonce_valid(ctx, &session->common, nonce, &age))
@@ -290,10 +271,10 @@ const fastd_method_t fastd_method_generic_gcm = {
 	.provides = method_provides,
 
 	.max_packet_size = method_max_packet_size,
-	.min_encrypt_head_space = method_min_encrypt_head_space,
-	.min_decrypt_head_space = method_min_decrypt_head_space,
-	.min_encrypt_tail_space = method_min_encrypt_tail_space,
-	.min_decrypt_tail_space = method_min_decrypt_tail_space,
+	.min_encrypt_head_space = sizeof(fastd_block128_t),
+	.min_decrypt_head_space = 0,
+	.min_encrypt_tail_space = sizeof(fastd_block128_t)-1,
+	.min_decrypt_tail_space = 2*sizeof(fastd_block128_t)-1,
 
 	.key_length = method_key_length,
 	.session_init = method_session_init,
diff --git a/src/methods/generic_gmac/generic_gmac.c b/src/methods/generic_gmac/generic_gmac.c
index c3ad0e6..71ee898 100644
--- a/src/methods/generic_gmac/generic_gmac.c
+++ b/src/methods/generic_gmac/generic_gmac.c
@@ -36,12 +36,10 @@ struct fastd_method_session_state {
 	const fastd_cipher_t *cipher;
 	const fastd_cipher_context_t *cipher_ctx;
 	fastd_cipher_state_t *cipher_state;
-	size_t ivlen;
 
 	const fastd_cipher_t *gmac_cipher;
 	const fastd_cipher_context_t *gmac_cipher_ctx;
 	fastd_cipher_state_t *gmac_cipher_state;
-	size_t gmac_ivlen;
 
 	const fastd_mac_t *ghash;
 	const fastd_mac_context_t *ghash_ctx;
@@ -93,19 +91,6 @@ static size_t method_max_packet_size(fastd_context_t *ctx) {
 }
 
 
-static size_t method_min_head_space(fastd_context_t *ctx UNUSED) {
-	return 0;
-}
-
-static size_t method_min_encrypt_tail_space(fastd_context_t *ctx UNUSED) {
-	return (sizeof(fastd_block128_t)-1);
-}
-
-static size_t method_min_decrypt_tail_space(fastd_context_t *ctx UNUSED) {
-	return (2*sizeof(fastd_block128_t)-1);
-}
-
-
 static size_t method_key_length(fastd_context_t *ctx, const char *name) {
 	const fastd_cipher_t *cipher = NULL;
 	const fastd_cipher_context_t *cctx;
@@ -116,7 +101,7 @@ static size_t method_key_length(fastd_context_t *ctx, const char *name) {
 	if (!cipher_get(ctx, name, &cipher, &cctx, &gmac_cipher, &gmac_cctx))
 		exit_bug(ctx, "generic-gmac: can't get cipher key length");
 
-	return cipher->key_length(ctx, cctx) + gmac_cipher->key_length(ctx, gmac_cctx);
+	return cipher->key_length + gmac_cipher->key_length;
 }
 
 static fastd_method_session_state_t* method_session_init(fastd_context_t *ctx, const char *name, const uint8_t *secret, bool initiator) {
@@ -128,19 +113,17 @@ static fastd_method_session_state_t* method_session_init(fastd_context_t *ctx, c
 		exit_bug(ctx, "generic-gmac: can't instanciate cipher");
 
 	session->cipher_state = session->cipher->init_state(ctx, session->cipher_ctx, secret);
-	session->ivlen = session->cipher->iv_length(ctx, session->cipher_state);
-	if (session->ivlen && session->ivlen <= COMMON_NONCEBYTES)
+	if (session->cipher->iv_length && session->cipher->iv_length <= COMMON_NONCEBYTES)
 		exit_bug(ctx, "generic-gmac: iv_length to small");
 
-	session->gmac_cipher_state = session->gmac_cipher->init_state(ctx, session->gmac_cipher_ctx, secret + session->cipher->key_length(ctx, session->cipher_ctx));
-	session->gmac_ivlen = session->gmac_cipher->iv_length(ctx, session->gmac_cipher_state);
-	if (session->gmac_ivlen <= COMMON_NONCEBYTES)
-		exit_bug(ctx, "generic-gmac: gmac cipher iv_length to small");
+	session->gmac_cipher_state = session->gmac_cipher->init_state(ctx, session->gmac_cipher_ctx, secret + session->cipher->key_length);
+	if (session->gmac_cipher->iv_length <= COMMON_NONCEBYTES)
+		exit_bug(ctx, "generic-gmac: GMAC cipher iv_length to small");
 
 	fastd_block128_t H;
 
-	uint8_t zeroiv[session->gmac_ivlen];
-	memset(zeroiv, 0, session->gmac_ivlen);
+	uint8_t zeroiv[session->gmac_cipher->iv_length];
+	memset(zeroiv, 0, session->gmac_cipher->iv_length);
 
 	session->gmac_cipher->crypt(ctx, session->gmac_cipher_state, &H, &ZERO_BLOCK, sizeof(fastd_block128_t), zeroiv);
 
@@ -201,19 +184,19 @@ static bool method_encrypt(fastd_context_t *ctx, fastd_peer_t *peer UNUSED, fast
 	fastd_block128_t *outblocks = out->data;
 	fastd_block128_t sig;
 
-	uint8_t gmac_nonce[session->gmac_ivlen];
-	memset(gmac_nonce, 0, session->gmac_ivlen);
+	uint8_t gmac_nonce[session->gmac_cipher->iv_length];
+	memset(gmac_nonce, 0, session->gmac_cipher->iv_length);
 	memcpy(gmac_nonce, session->common.send_nonce, COMMON_NONCEBYTES);
-	gmac_nonce[session->gmac_ivlen-1] = 1;
+	gmac_nonce[session->gmac_cipher->iv_length-1] = 1;
 
 	bool ok = session->gmac_cipher->crypt(ctx, session->gmac_cipher_state, outblocks, &ZERO_BLOCK, sizeof(fastd_block128_t), gmac_nonce);
 
 	if (ok) {
-		uint8_t nonce[session->ivlen];
-		if (session->ivlen) {
-			memset(nonce, 0, session->ivlen);
+		uint8_t nonce[session->cipher->iv_length];
+		if (session->cipher->iv_length) {
+			memset(nonce, 0, session->cipher->iv_length);
 			memcpy(nonce, session->common.send_nonce, COMMON_NONCEBYTES);
-			nonce[session->ivlen-1] = 1;
+			nonce[session->cipher->iv_length-1] = 1;
 		}
 
 		ok = session->cipher->crypt(ctx, session->cipher_state, outblocks+1, inblocks, n_blocks*sizeof(fastd_block128_t), nonce);
@@ -263,16 +246,16 @@ static bool method_decrypt(fastd_context_t *ctx, fastd_peer_t *peer, fastd_metho
 	if (!fastd_method_is_nonce_valid(ctx, &session->common, common_nonce, &age))
 		return false;
 
-	uint8_t gmac_nonce[session->gmac_ivlen];
-	memset(gmac_nonce, 0, session->gmac_ivlen);
+	uint8_t gmac_nonce[session->gmac_cipher->iv_length];
+	memset(gmac_nonce, 0, session->gmac_cipher->iv_length);
 	memcpy(gmac_nonce, common_nonce, COMMON_NONCEBYTES);
-	gmac_nonce[session->gmac_ivlen-1] = 1;
+	gmac_nonce[session->gmac_cipher->iv_length-1] = 1;
 
-	uint8_t nonce[session->ivlen];
-	if (session->ivlen) {
-		memset(nonce, 0, session->ivlen);
+	uint8_t nonce[session->cipher->iv_length];
+	if (session->cipher->iv_length) {
+		memset(nonce, 0, session->cipher->iv_length);
 		memcpy(nonce, common_nonce, COMMON_NONCEBYTES);
-		nonce[session->ivlen-1] = 1;
+		nonce[session->cipher->iv_length-1] = 1;
 	}
 
 	fastd_buffer_push_head(ctx, &in, COMMON_HEADBYTES);
@@ -321,10 +304,10 @@ const fastd_method_t fastd_method_generic_gmac = {
 	.provides = method_provides,
 
 	.max_packet_size = method_max_packet_size,
-	.min_encrypt_head_space = method_min_head_space,
-	.min_decrypt_head_space = method_min_head_space,
-	.min_encrypt_tail_space = method_min_encrypt_tail_space,
-	.min_decrypt_tail_space = method_min_decrypt_tail_space,
+	.min_encrypt_head_space = 0,
+	.min_decrypt_head_space = 0,
+	.min_encrypt_tail_space = sizeof(fastd_block128_t)-1,
+	.min_decrypt_tail_space = 2*sizeof(fastd_block128_t)-1,
 
 	.key_length = method_key_length,
 	.session_init = method_session_init,
diff --git a/src/methods/generic_poly1305/generic_poly1305.c b/src/methods/generic_poly1305/generic_poly1305.c
index fdad118..588e294 100644
--- a/src/methods/generic_poly1305/generic_poly1305.c
+++ b/src/methods/generic_poly1305/generic_poly1305.c
@@ -30,7 +30,7 @@
 #include <crypto_onetimeauth_poly1305.h>
 
 
-#define AUTHBLOCKS (block_count(crypto_onetimeauth_poly1305_KEYBYTES, sizeof(fastd_block128_t)))
+#define AUTHBLOCKS 2
 
 
 struct fastd_method_session_state {
@@ -39,7 +39,6 @@ struct fastd_method_session_state {
 	const fastd_cipher_t *cipher;
 	const fastd_cipher_context_t *cipher_ctx;
 	fastd_cipher_state_t *cipher_state;
-	size_t ivlen;
 };
 
 
@@ -74,26 +73,13 @@ static size_t method_max_packet_size(fastd_context_t *ctx) {
 	return (fastd_max_packet_size(ctx) + COMMON_HEADBYTES + crypto_onetimeauth_poly1305_BYTES);
 }
 
-static size_t method_min_encrypt_head_space(fastd_context_t *ctx UNUSED) {
-	return AUTHBLOCKS*sizeof(fastd_block128_t);
-}
-
-static size_t method_min_decrypt_head_space(fastd_context_t *ctx UNUSED) {
-	return AUTHBLOCKS*sizeof(fastd_block128_t) - crypto_onetimeauth_poly1305_BYTES;
-}
-
-static size_t method_min_tail_space(fastd_context_t *ctx UNUSED) {
-	return (sizeof(fastd_block128_t)-1);
-}
-
-
 static size_t method_key_length(fastd_context_t *ctx, const char *name) {
 	const fastd_cipher_t *cipher = NULL;
 	const fastd_cipher_context_t *cctx;
 	if (!cipher_get(ctx, name, &cipher, &cctx))
 		exit_bug(ctx, "generic-poly1305: can't get cipher key length");
 
-	return cipher->key_length(ctx, cctx);
+	return cipher->key_length;
 }
 
 static fastd_method_session_state_t* method_session_init(fastd_context_t *ctx, const char *name, const uint8_t *secret, bool initiator) {
@@ -106,8 +92,7 @@ static fastd_method_session_state_t* method_session_init(fastd_context_t *ctx, c
 
 	session->cipher_state = session->cipher->init_state(ctx, session->cipher_ctx, secret);
 
-	session->ivlen = session->cipher->iv_length(ctx, session->cipher_state);
-	if (session->ivlen <= COMMON_NONCEBYTES)
+	if (session->cipher->iv_length <= COMMON_NONCEBYTES)
 		exit_bug(ctx, "generic-poly1305: iv_length to small");
 
 	return session;
@@ -146,10 +131,10 @@ static bool method_encrypt(fastd_context_t *ctx, fastd_peer_t *peer UNUSED, fast
 	if (tail_len)
 		memset(in.data+in.len, 0, tail_len);
 
-	uint8_t nonce[session->ivlen];
-	memset(nonce, 0, session->ivlen);
+	uint8_t nonce[session->cipher->iv_length];
+	memset(nonce, 0, session->cipher->iv_length);
 	memcpy(nonce, session->common.send_nonce, COMMON_NONCEBYTES);
-	nonce[session->ivlen-1] = 1;
+	nonce[session->cipher->iv_length-1] = 1;
 
 	int n_blocks = block_count(in.len, sizeof(fastd_block128_t));
 
@@ -193,10 +178,10 @@ static bool method_decrypt(fastd_context_t *ctx, fastd_peer_t *peer, fastd_metho
 	if (((const uint8_t*)in.data)[COMMON_NONCEBYTES]) /* flags */
 		return false;
 
-	uint8_t nonce[session->ivlen];
-	memset(nonce, 0, session->ivlen);
+	uint8_t nonce[session->cipher->iv_length];
+	memset(nonce, 0, session->cipher->iv_length);
 	memcpy(nonce, in.data, COMMON_NONCEBYTES);
-	nonce[session->ivlen-1] = 1;
+	nonce[session->cipher->iv_length-1] = 1;
 
 	int64_t age;
 	if (!fastd_method_is_nonce_valid(ctx, &session->common, nonce, &age))
@@ -255,10 +240,10 @@ const fastd_method_t fastd_method_generic_poly1305 = {
 	.provides = method_provides,
 
 	.max_packet_size = method_max_packet_size,
-	.min_encrypt_head_space = method_min_encrypt_head_space,
-	.min_decrypt_head_space = method_min_decrypt_head_space,
-	.min_encrypt_tail_space = method_min_tail_space,
-	.min_decrypt_tail_space = method_min_tail_space,
+	.min_encrypt_head_space = AUTHBLOCKS*sizeof(fastd_block128_t),
+	.min_decrypt_head_space = AUTHBLOCKS*sizeof(fastd_block128_t) - crypto_onetimeauth_poly1305_BYTES,
+	.min_encrypt_tail_space = sizeof(fastd_block128_t)-1,
+	.min_decrypt_tail_space = sizeof(fastd_block128_t)-1,
 
 	.key_length = method_key_length,
 	.session_init = method_session_init,
diff --git a/src/methods/null/null.c b/src/methods/null/null.c
index 6874124..1b50cfb 100644
--- a/src/methods/null/null.c
+++ b/src/methods/null/null.c
@@ -41,10 +41,6 @@ static size_t method_max_packet_size(fastd_context_t *ctx) {
 	return fastd_max_packet_size(ctx);
 }
 
-static size_t method_min_head_tail_space(fastd_context_t *ctx UNUSED) {
-	return 0;
-}
-
 static size_t method_key_length(fastd_context_t *ctx UNUSED, const char *name UNUSED) {
 	return 0;
 }
@@ -91,10 +87,10 @@ const fastd_method_t fastd_method_null = {
 	.provides = method_provides,
 
 	.max_packet_size = method_max_packet_size,
-	.min_encrypt_head_space = method_min_head_tail_space,
-	.min_decrypt_head_space = method_min_head_tail_space,
-	.min_encrypt_tail_space = method_min_head_tail_space,
-	.min_decrypt_tail_space = method_min_head_tail_space,
+	.min_encrypt_head_space = 0,
+	.min_decrypt_head_space = 0,
+	.min_encrypt_tail_space = 0,
+	.min_decrypt_tail_space = 0,
 
 	.key_length = method_key_length,
 	.session_init = method_session_init,
diff --git a/src/methods/xsalsa20_poly1305/xsalsa20_poly1305.c b/src/methods/xsalsa20_poly1305/xsalsa20_poly1305.c
index 01c623a..f55db76 100644
--- a/src/methods/xsalsa20_poly1305/xsalsa20_poly1305.c
+++ b/src/methods/xsalsa20_poly1305/xsalsa20_poly1305.c
@@ -45,18 +45,6 @@ static size_t method_max_packet_size(fastd_context_t *ctx) {
 	return (fastd_max_packet_size(ctx) + COMMON_HEADBYTES + crypto_secretbox_xsalsa20poly1305_ZEROBYTES - crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES);
 }
 
-static size_t method_min_encrypt_head_space(fastd_context_t *ctx UNUSED) {
-	return crypto_secretbox_xsalsa20poly1305_ZEROBYTES;
-}
-
-static size_t method_min_decrypt_head_space(fastd_context_t *ctx UNUSED) {
-	return (crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES - COMMON_HEADBYTES);
-}
-
-static size_t method_min_tail_space(fastd_context_t *ctx UNUSED) {
-	return 0;
-}
-
 
 static size_t method_key_length(fastd_context_t *ctx UNUSED, const char *name UNUSED) {
 	return crypto_secretbox_xsalsa20poly1305_KEYBYTES;
@@ -173,10 +161,10 @@ const fastd_method_t fastd_method_xsalsa20_poly1305 = {
 	.provides = method_provides,
 
 	.max_packet_size = method_max_packet_size,
-	.min_encrypt_head_space = method_min_encrypt_head_space,
-	.min_decrypt_head_space = method_min_decrypt_head_space,
-	.min_encrypt_tail_space = method_min_tail_space,
-	.min_decrypt_tail_space = method_min_tail_space,
+	.min_encrypt_head_space = crypto_secretbox_xsalsa20poly1305_ZEROBYTES,
+	.min_decrypt_head_space = crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES - COMMON_HEADBYTES,
+	.min_encrypt_tail_space = 0,
+	.min_decrypt_tail_space = 0,
 
 	.key_length = method_key_length,
 	.session_init = method_session_init,