diff --git a/aead.h b/aead.h
index b8f150d..aa5b51c 100644
--- a/aead.h
+++ b/aead.h
@@ -23,4 +23,6 @@ struct lc_aead_impl {
 		    const uint8_t *, size_t);
 	int	(*open)(uint8_t *, size_t *, void *, const uint8_t *, size_t,
 		    const uint8_t *, size_t);
+
+	size_t	  blocklen;
 };
diff --git a/aead_chacha20_poly1305.c b/aead_chacha20_poly1305.c
index a02552f..6875e21 100644
--- a/aead_chacha20_poly1305.c
+++ b/aead_chacha20_poly1305.c
@@ -419,11 +419,15 @@ xchacha20_poly1305_open(uint8_t *out, size_t *outlen, void *initparams,
 static struct lc_aead_impl	chacha20_poly1305_impl = {
 	.seal = &chacha20_poly1305_seal,
 	.open = &chacha20_poly1305_open,
+
+	.blocklen = LC_CHACHA20_BLOCKLEN,
 };
 
 static struct lc_aead_impl	xchacha20_poly1305_impl = {
 	.seal = &xchacha20_poly1305_seal,
 	.open = &xchacha20_poly1305_open,
+
+	.blocklen = LC_XCHACHA20_BLOCKLEN,
 };
 
 const struct lc_aead_impl *
diff --git a/auth.h b/auth.h
index 945cdd1..35924b7 100644
--- a/auth.h
+++ b/auth.h
@@ -26,6 +26,9 @@ struct lc_auth_impl {
 
 	void	*(*ctx_new)(void);
 	void	 (*ctx_free)(void *);
+
+	size_t	   blocklen;
+	size_t	   taglen;
 };
 
 struct lc_auth_ctx {
diff --git a/auth_poly1305.c b/auth_poly1305.c
index dff2c72..ce4c4c8 100644
--- a/auth_poly1305.c
+++ b/auth_poly1305.c
@@ -165,6 +165,9 @@ static struct lc_auth_impl	poly1305_impl = {
 
 	.ctx_new = &poly1305_ctx_new,
 	.ctx_free = NULL,
+
+	.blocklen = LC_POLY1305_BLOCKLEN,
+	.taglen = LC_POLY1305_TAGLEN,
 };
 
 const struct lc_auth_impl *
diff --git a/cipher.h b/cipher.h
index 321f40b..497de0a 100644
--- a/cipher.h
+++ b/cipher.h
@@ -35,6 +35,8 @@ struct lc_cipher_impl {
 
 	void	*(*ctx_new)(void);
 	void	 (*ctx_free)(void *);
+
+	size_t	   blocklen;
 };
 
 struct lc_cipher_ctx {
diff --git a/cipher_chacha20.c b/cipher_chacha20.c
index fcd2aaa..d8e9b83 100644
--- a/cipher_chacha20.c
+++ b/cipher_chacha20.c
@@ -229,6 +229,8 @@ static struct lc_cipher_impl	chacha20_impl = {
 
 	.ctx_new = &chacha20_ctx_new,
 	.ctx_free = NULL,
+
+	.blocklen = LC_CHACHA20_BLOCKLEN,
 };
 
 static struct lc_cipher_impl	xchacha20_impl = {
@@ -244,6 +246,8 @@ static struct lc_cipher_impl	xchacha20_impl = {
 
 	.ctx_new = &chacha20_ctx_new,
 	.ctx_free = NULL,
+
+	.blocklen = LC_XCHACHA20_BLOCKLEN,
 };
 
 const struct lc_cipher_impl *