refactored sodium_crypto_secretbox() into separate source file.

src/Makefile

@@ -3,15 +3,20 @@ CFLAGS=-Wall
 LDFLAGS=-lsodium
 LDFLAGS_LIB=-I/usr/include/exim4 -fpic -shared -export-dynamic
 
-.PHONY: clean
+.PHONY: clean libs
 
-.DEFAULT_GOAL := libexim-kitencrypt-dlfunc.so
+.DEFAULT_GOAL := libs
 
 libexim-kitencrypt-dlfunc.so: libexim-kitencrypt-dlfunc.c recipient_pk.h
 	$(CC) $(CFLAGS) $(LDFLAGS) $(LDFLAGS_LIB) -o $@ $<
 
+libexim-encrypt-dlfunc.so: libexim-encrypt-dlfunc.c
+	$(CC) $(CFLAGS) $(LDFLAGS) $(LDFLAGS_LIB) -o $@ $<
+
 genkey: genkey.c
 	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $<
 
 clean:
-	rm -f libexim-kitencrypt-dlfunc.so
+	rm -f libexim-kitencrypt-dlfunc.so libexim-encrypt-dlfunc.so
+
+libs: libexim-kitencrypt-dlfunc.so libexim-encrypt-dlfunc.so

src/libexim-encrypt-dlfunc.c

@@ -0,0 +1,69 @@
+#include <stdlib.h>
+#include <string.h>
+#include <strings.h>
+#include <sodium.h>
+
+/* Local encryption key */
+#include "recipient_pk.h"
+
+/* Exim4 dlfunc API header */
+#include <local_scan.h>
+
+/*
+ * Encrypt the second argument with password from the first argument
+ */
+int sodium_crypto_secretbox(uschar ** yield, int argc, uschar * argv[])
+{
+	if (sodium_init() == -1) {
+		*yield = string_copy(US "Unable to initialize libsodium");
+		return ERROR;
+	}
+	if (argc != 2) {
+		*yield =
+		    string_sprintf
+		    ("Wrong number of arguments (got %i, expected 2)", argc);
+		return ERROR;
+	}
+	// get password
+	unsigned char *password = argv[0];
+	size_t passwordlen = strlen((const char *)password);
+
+	// get cleartext message
+	unsigned char *message = argv[1];
+	size_t messagelen = strlen((const char *)message);
+
+	/*
+	 * Derive a key from the password.
+	 * This operations needs to be fast (exim holds no state, this might be called once or mutliple times per email).
+	 * Collisions avoidance or brute force arracks are not a concern here.
+	 */
+	unsigned char keybytes[crypto_secretbox_KEYBYTES];
+	sodium_memzero(keybytes, crypto_secretbox_KEYBYTES);
+	crypto_generichash(keybytes, crypto_secretbox_KEYBYTES,
+			   password, passwordlen, NULL, 0);
+
+	// prepare buffer for ciphertext
+	unsigned int cipherlen = messagelen + crypto_secretbox_MACBYTES;
+	unsigned char *ciphertext = malloc(cipherlen);
+	sodium_memzero(ciphertext, cipherlen);
+
+	// encrypt message
+	unsigned char nonce[crypto_secretbox_NONCEBYTES];
+	randombytes_buf(nonce, sizeof nonce);
+	crypto_secretbox_easy(ciphertext, message, messagelen, nonce, keybytes);
+
+	// base64-encode the ciphertext
+	unsigned int outputsize = sodium_base64_ENCODED_LEN(cipherlen,
+							    sodium_base64_VARIANT_ORIGINAL);
+	unsigned char *outstring = malloc(outputsize);
+	sodium_memzero(outstring, outputsize);
+	sodium_bin2base64((char *const)outstring, outputsize,
+			  ciphertext, cipherlen,
+			  sodium_base64_VARIANT_ORIGINAL);
+	free(ciphertext);
+
+	// return base64-encoded ciphertext
+	*yield = string_copy(outstring);
+	free(outstring);
+	return OK;
+}

src/libexim-kitencrypt-dlfunc.c

@@ -40,9 +40,8 @@ int sodium_crypto_box_seal_kit(uschar ** yield, int argc, uschar * argv[])
 	crypto_box_seal(ciphertext, message, messagelen, recipient_pk);
 
 	// base64-encode the ciphertext
-	unsigned int outputsize =
-	    sodium_base64_ENCODED_LEN(cipherlen,
-				      sodium_base64_VARIANT_ORIGINAL);
+	unsigned int outputsize = sodium_base64_ENCODED_LEN(cipherlen,
+							    sodium_base64_VARIANT_ORIGINAL);
 	unsigned char *outstring = malloc(outputsize);
 	sodium_memzero(outstring, outputsize);
 
@@ -57,51 +56,3 @@ int sodium_crypto_box_seal_kit(uschar ** yield, int argc, uschar * argv[])
 
 	return OK;
 }
-
-/*
- * Encrypt first argument with passworf from the second argument
- */
-/*
-// https://libsodium.gitbook.io/doc/hashing/short-input_hashing
-int sodium_crypto_box_seal_password(uschar **yield, int argc, uschar *argv[]) {
-	size_t messagelen;
-	unsigned char * message;
-
-	if (sodium_init() == -1 ) {
-		*yield = string_copy(US"Unable to initialize libsodium");
-		return ERROR;
-	}
-	if (argc != 2) {
-		*yield = string_sprintf("Wrong number of arguments (got %i, expected 1)", argc);
-		return ERROR;
-	}
-
-	// get cleartext message
-	message = argv[0];
-	messagelen = strlen((const char *) message);
-
-	// prepare buffer for ciphertext
-	unsigned int cipherlen = messagelen + crypto_box_SEALBYTES;
-	unsigned char * ciphertext = malloc(cipherlen);
-	explicit_bzero(ciphertext, cipherlen);
-
-	// encrypt message
-	crypto_box_seal(ciphertext, message, messagelen, recipient_pk);
-
-	// base64-encode the ciphertext
-	unsigned int outputsize = sodium_base64_ENCODED_LEN(cipherlen, sodium_base64_VARIANT_ORIGINAL);
-	unsigned char * outstring = malloc(outputsize);
-	explicit_bzero(outstring, outputsize);
-
-	sodium_bin2base64((char * const) outstring, outputsize,
-			ciphertext, cipherlen,
-			sodium_base64_VARIANT_ORIGINAL);
-	free(ciphertext);
-
-	// return base64-encoded ciphertext
-	*yield = string_copy(outstring);
-	free(outstring);
-
-	return OK;
-}
-*/