Improve the man page for incremental crypto_lock

This fixes the function types in the SYNOPSIS section and removes a
stray macro.

This adds information about the incremental interface to the DESCRIPTION
section.  In particular, it documents the tradeoff (convenience of the
interface vs. performance loss on forged messages).

INCREMENTAL INTERFACE, which seemed to just be a subset to the EXAMPLES
section, got lowered into a second-level heading.

diff --git a/doc/man/man3/crypto_lock.3monocypher b/doc/man/man3/crypto_lock.3monocypher
index 162ce706808ac5d5f3726ec5dc8a086c41b384ea..fc56026bd0dc125bd2c86ee33250cd3a611d49bb 100644 (file)
--- a/doc/man/man3/crypto_lock.3monocypher
+++ b/doc/man/man3/crypto_lock.3monocypher
@@ -33,35 +33,34 @@
 .Fc
 .Ft void
 .Fo crypto_lock_auth
-.Fa crypto_lock_ctx *ctx
-.Fa const uint8_t *ad
-.Fa size_t ad_size
+.Fa "crypto_lock_ctx *ctx"
+.Fa "const uint8_t *ad"
+.Fa "size_t ad_size"
 .Fc
 .Ft void
 .Fo crypto_lock_update
-.Fa crypto_lock_ctx *ctx
-.Fa uint8_t *cipher_text
-.Fa const uint8_t *plain_text
-.Fa size_t text_size
+.Fa "crypto_lock_ctx *ctx"
+.Fa "uint8_t *cipher_text"
+.Fa "const uint8_t *plain_text"
+.Fa "size_t text_size"
 .Fc
 .Ft void
 .Fo crypto_lock_final
-.Fa crypto_lock_ctx *ctx
-.Fa uint8_t mac[16]
+.Fa "crypto_lock_ctx *ctx"
+.Fa "uint8_t mac[16]"
 .Fc
 .Ft void
-.Fo crypto_unlock_update
-.Fa crypto_lock_ctx *ctx
-.Fa uint8_t *plain_text
-.Fa const uint8_t *cipher_text
-.Fa size_t text_size
+.Fo "crypto_unlock_update
+.Fa "crypto_lock_ctx *ctx"
+.Fa "uint8_t *plain_text"
+.Fa "const uint8_t *cipher_text"
+.Fa "size_t text_size"
 .Fc
 .Ft int
 .Fo crypto_unlock_final
-.Fa crypto_lock_ctx *ctx
-.Fa const uint8_t mac[16]
+.Fa "crypto_lock_ctx *ctx"
+.Fa "const uint8_t mac[16]"
 .Fc
-.F
 .Sh DESCRIPTION
 Encryption makes your messages unreadable to eavesdroppers.
 Authentication ascertain the origin and integrity of the messages you
@@ -72,7 +71,7 @@ authentication, you can fall prey to forgeries (messages that look
 legitimate, but actually come from an attacker).
 A clever attacker may even leverage forgeries to steal your secrets.
 Always authenticate your messages.
-.Pp
+.Ss Direct interface
 The
 .Fn crypto_lock
 function encrypts and authenticates a plaintext.
@@ -147,14 +146,75 @@ If the message is genuine, the
 .Fn crypto_aead_unlock
 function decrypts the ciphertext.
 .Em Always check the return value .
+.Ss Incremental interface
+The incremental interface allows to split up decryption and
+authentication of larger messages too large to fit into a single buffer
+or to handle individual pieces of data located in different buffers.
+.Pp
+The arguments are the same as described for the direct interface.
+It instead uses three steps:
+.Bl -bullet
+.It
+initialisation, where we set up a context for encryption/decryption and
+authentication;
+.It
+update, where we encrypt/decrypt and incrementally generate the MAC;
+.It
+final, where we generate/check the MAC.
+.El
+.Pp
+Because the incremental interface interleaves both encryption and
+authentication,
+.Sy a message with a mismatched MAC is three times slower
+to process than when using the direct interface.
+The direct interface checks the MAC first and only then proceeds to
+decrypt.
+If you expect to frequently encounter messages whose MAC mismatches,
+especially large messages, you may want to forgo the incremental
+interface for a different approach.
+.Pp
+.Sy Both encryption and decryption
+are initialized with
+.Fn crypto_lock_init .
+If you need to authenticate data without encrypting like with
+.Xr crypto_aead_lock 3monocypher ,
+plaintext data can be authenticated with
+.Fn crypto_lock_auth .
+Calls to
+.Fn crypto_lock_auth
+.Em can
+be interleaved with calls to
+.Fn crypto_lock_update
+and
+.Fn crypto_unlock_update .
+.Pp
+.Sy For encryption,
+.Fn crypto_lock_update
+authenticates and encrypts the data;
+.Fn crypto_lock_final
+generates the MAC.
+.Sy For decryption ,
+.Fn crypto_unlock_update
+authenticates and decrypts the data;
+.Fn crypto_unlock_final
+checks the MAC.
+.Em Always check the return value .
 .Sh RETURN VALUES
 The
-.Fn crypto_lock
-function returns nothing.
-It cannot fail.
+.Fn crypto_lock ,
+.Fn crypto_lock_init ,
+.Fn crypto_lock_auth ,
+.Fn crypto_lock_update ,
+and
+.Fn crypto_lock_final
+functions return nothing.
+They cannot fail.
+.Pp
 The
 .Fn crypto_unlock
-function returns 0 on success or -1 if the message was corrupted
+and
+.Fn crypto_unlock_final
+functions return 0 on success or -1 if the message was corrupted
 (i.e.
 .Fa mac
 mismatched the combination of
@@ -168,6 +228,7 @@ of the expected
 .Fa cipher_text )
 or an attacker's interference.
 .Sh EXAMPLES
+.Ss Direct interface
 Encryption:
 .Bd -literal -offset indent
 uint8_t key[32], nonce[24];
@@ -210,7 +271,7 @@ if (ret != 0) {
          */
 }
 .Ed
-.Sh INCREMENTAL INTERFACE
+.Ss Incremental interface
 Useful for decrypting huge inputs.
 This time, decryption is performed regardless of whether the message
 is corrupted or not.