Put just a touch of pointer magick in a crypt module. Also put const modifiers here and there.

src/crypt.c

@@ -1,7 +1,7 @@
 #include "crypt.h"
 
-#include <sodium/utils.h>
 #include <stdlib.h>
+#include <string.h>
 
 int crypt_key_gen(crypt_key_t *const k) {
     if (crypto_kx_keypair(k->kx_pub, k->kx_sec) < 0) {
@@ -17,7 +17,7 @@ int crypt_key_gen(crypt_key_t *const k) {
     return 0;
 }
 
-int crypt_key_from_hex(crypt_key_t *const k, char phex[CRYPT_PKEY_HEXLEN], char shex[CRYPT_SKEY_HEXLEN]) {
+int crypt_key_from_hex(crypt_key_t *const k, const char phex[CRYPT_PKEY_HEXLEN], const char shex[CRYPT_SKEY_HEXLEN]) {
     if (sodium_hex2bin(k->kx_pub, CRYPT_KX_PKEY_LEN, phex, CRYPT_KX_PKEY_LEN * 2, NULL, NULL, NULL) < 0)
         return -1;
     if (sodium_hex2bin(k->kx_sec, CRYPT_KX_SKEY_LEN, shex, CRYPT_KX_SKEY_LEN * 2, NULL, NULL, NULL) < 0)
@@ -32,7 +32,7 @@ int crypt_key_from_hex(crypt_key_t *const k, char phex[CRYPT_PKEY_HEXLEN], char
     return 0;
 }
 
-int crypt_key_from_hex_public(crypt_key_t *const k, char phex[CRYPT_PKEY_HEXLEN]) {
+int crypt_key_from_hex_public(crypt_key_t *const k, const char phex[CRYPT_PKEY_HEXLEN]) {
     if (sodium_hex2bin(k->kx_pub, CRYPT_KX_PKEY_LEN, phex, CRYPT_KX_PKEY_LEN * 2, NULL, NULL, NULL) < 0)
         return -1;
     if (sodium_hex2bin(k->sign_pub, CRYPT_SIGN_PKEY_LEN, phex+(CRYPT_KX_PKEY_LEN * 2), CRYPT_SIGN_PKEY_LEN * 2, NULL, NULL, NULL) < 0)
@@ -104,14 +104,23 @@ int crypt_store_key(const crypt_key_t *const k, FILE *const pub, FILE *const sec
     return 0;
 }
 
-unsigned char *crypt_hello(const crypt_key_t *const own, long long unsigned int *const sign_len) {
+unsigned char *crypt_hello(const crypt_key_t *const own) {
-    char pub_hex[CRYPT_PKEY_HEXLEN];
+    unsigned char *hello = (unsigned char *)malloc(CRYPT_HELLO_LEN * sizeof(unsigned char));
-    crypt_key_export_public(own, pub_hex);
+
-    *sign_len = crypto_sign_BYTES + CRYPT_PKEY_HEXLEN;
+    crypt_key_export_public(own, (char *const)hello);
-    unsigned char *sign = (unsigned char *)malloc(*sign_len * sizeof(unsigned char));
+
-    if (crypto_sign(sign, sign_len, (const unsigned char *)pub_hex, CRYPT_PKEY_HEXLEN, own->sign_sec) == -1)
+    if (crypto_sign_detached(hello+CRYPT_PKEY_HEXLEN, NULL, (const unsigned char *)hello, CRYPT_PKEY_HEXLEN, own->sign_sec) == -1) {
         return NULL;
-    return sign;
+    }
+
+    return hello;
+}
+
+int crypt_hello_verify(const unsigned char *const hello, crypt_key_t *const remote) {
+    if (crypt_key_from_hex_public(remote, (const char *const)hello) < 0)
+        return -1;
+
+    return crypto_sign_verify_detached(hello+CRYPT_PKEY_HEXLEN, (const unsigned char *const)hello, CRYPT_PKEY_HEXLEN, remote->sign_pub);
 }
 
 int crypt_session_init(crypt_session_t *const s, const crypt_key_t *const own, crypt_key_t *const remote, const bool is_client) {

src/crypt.h

@@ -8,10 +8,15 @@
 
 #define CRYPT_KX_PKEY_LEN crypto_kx_PUBLICKEYBYTES
 #define CRYPT_KX_SKEY_LEN crypto_kx_SECRETKEYBYTES
+
 #define CRYPT_SIGN_PKEY_LEN crypto_sign_PUBLICKEYBYTES
 #define CRYPT_SIGN_SKEY_LEN crypto_sign_SECRETKEYBYTES
+#define CRYPT_SIGN_LEN crypto_sign_BYTES
+
 #define CRYPT_SESS_KEY_LEN crypto_kx_SESSIONKEYBYTES
 
+#define CRYPT_HELLO_LEN CRYPT_PKEY_HEXLEN + CRYPT_SIGN_LEN
+
 #define CRYPT_PKEY_HEXLEN (CRYPT_KX_PKEY_LEN + CRYPT_SIGN_PKEY_LEN) * 2
 #define CRYPT_SKEY_HEXLEN (CRYPT_SIGN_PKEY_LEN + CRYPT_SIGN_SKEY_LEN) * 2
 
@@ -27,9 +32,9 @@ typedef struct crypt_key_t {
 // Generates the new pairs of a key exchange and sign keys.
 int crypt_key_gen(crypt_key_t *const k);
 // Initialise a crypt_key_t with a provided hex representaions of public and secret keys.
-int crypt_key_from_hex(crypt_key_t *const k, char phex[CRYPT_PKEY_HEXLEN], char shex[CRYPT_SKEY_HEXLEN]);
+int crypt_key_from_hex(crypt_key_t *const k, const char phex[CRYPT_PKEY_HEXLEN], const char shex[CRYPT_SKEY_HEXLEN]);
 // Initialise a crypt_key_t with a provided hex representaion of just a public key. Used for remote keys.
-int crypt_key_from_hex_public(crypt_key_t *const k, char phex[CRYPT_PKEY_HEXLEN]);
+int crypt_key_from_hex_public(crypt_key_t *const k, const char phex[CRYPT_PKEY_HEXLEN]);
 
 // Securely erase the fields of a crypt_key_t struct.
 void crypt_key_destroy(crypt_key_t *const k);
@@ -48,7 +53,9 @@ int crypt_store_key(const crypt_key_t *const k, FILE *const pub, FILE *const sec
 
 // Returns a hello packet consisting of a public key and its sign.
 // The packet is sign_len long.
-unsigned char *crypt_hello(const crypt_key_t *const own, long long unsigned int *const sign_len);
+unsigned char *crypt_hello(const crypt_key_t *const own);
+// Verify a hello message. It only shows that a remote public key's sign is ok.
+int crypt_hello_verify(const unsigned char *const hello, crypt_key_t *const remote);
 
 // Stores symmetric keys used for a data encryption in both directions
 // and a remote public key.

src/main.c

@@ -48,8 +48,6 @@ int main(int argc, char **argv) {
 
     crypt_store_key(&own, fp, fs);
 
-    printf("p1 = [%s]\ns1 = [%s]\n", phex, shex);
-
 
     fflush(fp);
     fflush(fs);
@@ -63,11 +61,14 @@ int main(int argc, char **argv) {
     crypt_key_export_public(&ownr, phexr);
     crypt_key_export_secret(&ownr, shexr);
 
-    printf("p2 = [%s]\ns2 = [%s]\n", phexr, shexr);
-
     fclose(fp);
     fclose(fs);
 
+    unsigned char *h = crypt_hello(&own);
+
+    int o = crypt_hello_verify(h, &ownr);
+    printf("o = %i\n", o);
+
     crypt_key_destroy(&own);
     crypt_key_destroy(&ownr);