Oh, because of goto used some var can never be presented, so lets move them right before the first use of a goto.

src/crypt.c

@@ -1,8 +1,9 @@
 #include "crypt.h"
 
 #include <stdlib.h>
+#include <string.h>
 
-int crypt_key_gen(crypt_key_t *k) {
+int crypt_key_gen(crypt_key_t *const k) {
     if (crypto_kx_keypair(k->kx_pub, k->kx_sec) < 0) {
         return -1;
     }
@@ -16,19 +17,14 @@ int crypt_key_gen(crypt_key_t *k) {
     return 0;
 }
 
-int crypt_key_from_hex(crypt_key_t *k, char phex[CRYPT_PUBKEY_HEXSIZE], char shex[CRYPT_SECKEY_HEXSIZE]) {
-    int res = 0;
-    res = sodium_hex2bin(k->kx_pub, crypto_kx_PUBLICKEYBYTES, phex, crypto_kx_PUBLICKEYBYTES * 2, NULL, NULL, NULL);
-    if (res < 0)
+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;
-    res = sodium_hex2bin(k->kx_sec, crypto_kx_SECRETKEYBYTES, shex, crypto_kx_SECRETKEYBYTES * 2, NULL, NULL, NULL);
-    if (res < 0)
+    if (sodium_hex2bin(k->kx_sec, CRYPT_KX_SKEY_LEN, shex, CRYPT_KX_SKEY_LEN * 2, NULL, NULL, NULL) < 0)
         return -1;
-    res = sodium_hex2bin(k->sign_pub, crypto_sign_PUBLICKEYBYTES, phex+(crypto_kx_PUBLICKEYBYTES * 2), crypto_sign_PUBLICKEYBYTES * 2, NULL, NULL, NULL);
-    if (res < 0)
+    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)
         return -1;
-    res = sodium_hex2bin(k->sign_sec, crypto_sign_SECRETKEYBYTES, shex+(crypto_kx_SECRETKEYBYTES * 2), crypto_sign_SECRETKEYBYTES * 2, NULL, NULL, NULL);
-    if (res < 0)
+    if (sodium_hex2bin(k->sign_sec, CRYPT_SIGN_SKEY_LEN, shex+(CRYPT_KX_SKEY_LEN * 2), CRYPT_SIGN_SKEY_LEN * 2, NULL, NULL, NULL) < 0)
         return -1;
 
     k->hasSecKey = true;
@@ -36,13 +32,10 @@ int crypt_key_from_hex(crypt_key_t *k, char phex[CRYPT_PUBKEY_HEXSIZE], char she
     return 0;
 }
 
-int crypt_key_from_hex_public(crypt_key_t *k, char phex[CRYPT_PUBKEY_HEXSIZE]) {
-    int res = 0;
-    res = sodium_hex2bin(k->kx_pub, crypto_kx_PUBLICKEYBYTES, phex, crypto_kx_PUBLICKEYBYTES * 2, NULL, NULL, NULL);
-    if (res < 0)
+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;
-    res = sodium_hex2bin(k->sign_pub, crypto_sign_PUBLICKEYBYTES, phex+(crypto_kx_PUBLICKEYBYTES * 2), crypto_sign_PUBLICKEYBYTES * 2, NULL, NULL, NULL);
-    if (res < 0)
+    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)
         return -1;
 
     k->hasSecKey = false;
@@ -50,30 +43,108 @@ int crypt_key_from_hex_public(crypt_key_t *k, char phex[CRYPT_PUBKEY_HEXSIZE]) {
     return 0;
 }
 
-void crypt_key_export_public(crypt_key_t *k, char hex[CRYPT_PUBKEY_HEXSIZE]) {
-    sodium_bin2hex(hex, crypto_kx_PUBLICKEYBYTES * 2 + 1, k->kx_pub, crypto_kx_PUBLICKEYBYTES);
-    sodium_bin2hex(hex+(crypto_kx_PUBLICKEYBYTES * 2), crypto_sign_PUBLICKEYBYTES * 2 + 1, k->sign_pub, crypto_sign_PUBLICKEYBYTES);
+void crypt_key_destroy(crypt_key_t *const k) {
+    sodium_memzero(k->kx_pub, CRYPT_KX_PKEY_LEN);
+    sodium_memzero(k->kx_sec, CRYPT_KX_SKEY_LEN);
+    sodium_memzero(k->sign_pub, CRYPT_SIGN_PKEY_LEN);
+    sodium_memzero(k->sign_sec, CRYPT_SIGN_SKEY_LEN);
 }
 
-void crypt_key_export_secret(crypt_key_t *k, char hex[CRYPT_SECKEY_HEXSIZE]) {
-    sodium_bin2hex(hex, crypto_kx_SECRETKEYBYTES * 2 + 1, k->kx_sec, crypto_kx_SECRETKEYBYTES);
-    sodium_bin2hex(hex+(crypto_kx_SECRETKEYBYTES * 2), crypto_sign_SECRETKEYBYTES * 2 + 1, k->sign_sec, crypto_sign_SECRETKEYBYTES);
+int crypt_key_export_public(const crypt_key_t *const k, char hex[CRYPT_PKEY_HEXLEN]) {
+    if (sodium_bin2hex(hex, CRYPT_KX_PKEY_LEN * 2 + 1, k->kx_pub, CRYPT_KX_PKEY_LEN) == NULL)
+        return -1;
+    if (sodium_bin2hex(hex+(CRYPT_KX_PKEY_LEN * 2), CRYPT_SIGN_PKEY_LEN * 2 + 1, k->sign_pub, CRYPT_SIGN_PKEY_LEN) == NULL)
+        return -1;
+
+    return 0;
 }
 
-void crypt_store_public_key(crypt_key_t *k, FILE *out_file) {
-    char phex[CRYPT_PUBKEY_HEXSIZE+1];
-    crypt_key_export_public(k, phex);
-    int o = fwrite(phex, sizeof(phex[0]), CRYPT_PUBKEY_HEXSIZE, out_file);
-    printf("%li %i | %i\n", sizeof(phex[0]), CRYPT_PUBKEY_HEXSIZE, o);
+int crypt_key_export_secret(const crypt_key_t *const k, char hex[CRYPT_SKEY_HEXLEN]) {
+    if (!k->hasSecKey)
+        return -1;
+
+    if (sodium_bin2hex(hex, CRYPT_KX_SKEY_LEN * 2 + 1, k->kx_sec, CRYPT_KX_SKEY_LEN) == NULL)
+        return -1;
+    if (sodium_bin2hex(hex+(CRYPT_KX_SKEY_LEN * 2), CRYPT_SIGN_SKEY_LEN * 2 + 1, k->sign_sec, CRYPT_SIGN_SKEY_LEN) == NULL)
+        return -1;
+
+    return 0;
 }
 
-void crypt_store_secret_key(crypt_key_t *k, FILE *out_file) {
-    char shex[CRYPT_SECKEY_HEXSIZE+1];
-    crypt_key_export_secret(k, shex);
-    fwrite(shex, sizeof(shex[0]), CRYPT_SECKEY_HEXSIZE, out_file);
+int crypt_load_key(crypt_key_t *const k, FILE *const pub, FILE *const sec) {
+    if (pub == NULL || sec == NULL)
+        return -1;
+
+    char phex[CRYPT_PKEY_HEXLEN], shex[CRYPT_SKEY_HEXLEN];
+
+    if (fread(phex, sizeof(phex[0]), CRYPT_PKEY_HEXLEN, pub) != CRYPT_PKEY_HEXLEN)
+        return -1;
+    if (fread(shex, sizeof(shex[0]), CRYPT_SKEY_HEXLEN, sec) != CRYPT_SKEY_HEXLEN)
+        return -1;
+
+    return crypt_key_from_hex(k, phex, shex);
 }
 
-int crypt_session_init(crypt_session_t *s, crypt_key_t *own, crypt_key_t *remote, bool is_client) {
+int crypt_store_key(const crypt_key_t *const k, FILE *const pub, FILE *const sec) {
+    if (!k->hasSecKey || pub == NULL || sec == NULL)
+        return -1;
+
+    char phex[CRYPT_PKEY_HEXLEN], shex[CRYPT_SKEY_HEXLEN];
+
+    if (crypt_key_export_public(k, phex) < 0)
+        return -1;
+    if (crypt_key_export_secret(k, shex) < 0)
+        return -1;
+
+    if (fwrite(phex, sizeof(phex[0]), CRYPT_PKEY_HEXLEN, pub) != CRYPT_PKEY_HEXLEN)
+        return -1;
+    if (fwrite(shex, sizeof(shex[0]), CRYPT_SKEY_HEXLEN, sec) != CRYPT_SKEY_HEXLEN)
+        return -1;
+
+    return 0;
+}
+
+unsigned char *crypt_hello(const crypt_key_t *const own) {
+    unsigned char *hello = (unsigned char *)malloc(CRYPT_HELLO_LEN * sizeof(unsigned char));
+
+    crypt_key_export_public(own, (char *const)hello);
+
+    if (crypto_sign_detached(hello+CRYPT_PKEY_HEXLEN, NULL, (const unsigned char *)hello, CRYPT_PKEY_HEXLEN, own->sign_sec) == -1) {
+        return NULL;
+    }
+
+    randombytes_buf(hello+CRYPT_PKEY_HEXLEN+CRYPT_SIGN_LEN, CRYPT_NONCEHALF_LEN);
+
+    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;
+
+    if (crypto_sign_verify_detached(hello+CRYPT_PKEY_HEXLEN, (const unsigned char *const)hello, CRYPT_PKEY_HEXLEN, remote->sign_pub))
+        return -1;
+
+    return 0;
+}
+
+unsigned char *crypt_hello_get_nonce(const unsigned char *const own_hello, const unsigned char *const remote_hello, bool is_client) {
+    unsigned char *nonce = (unsigned char *)malloc(CRYPT_NONCE_LEN * sizeof(unsigned char));
+    if (nonce == NULL)
+        return NULL;
+
+    const unsigned char *first = NULL, *second = NULL;
+
+    first = (is_client ? own_hello : remote_hello) + CRYPT_PKEY_HEXLEN+CRYPT_SIGN_LEN;
+    second = (is_client ? remote_hello : own_hello) + CRYPT_PKEY_HEXLEN+CRYPT_SIGN_LEN;
+
+    memcpy(nonce, first, CRYPT_NONCEHALF_LEN);
+    memcpy(nonce+CRYPT_NONCEHALF_LEN, second, CRYPT_NONCEHALF_LEN);
+
+    return nonce;
+}
+
+int crypt_session_init(crypt_session_t *const s, const crypt_key_t *const own, crypt_key_t *const remote, const unsigned char *const nonce, bool is_client) {
     if (is_client) {
         if (crypto_kx_client_session_keys(s->rx, s->tx, own->kx_pub, own->kx_sec, remote->kx_pub) != 0) {
             fprintf(stderr, "Failed to instantiate a client session.\n");
@@ -88,5 +159,33 @@ int crypt_session_init(crypt_session_t *s, crypt_key_t *own, crypt_key_t *remote
 
     s->remote_key = remote;
 
+    memcpy(s->nonce, nonce, CRYPT_NONCE_LEN);
+
     return 0;
+}
+
+unsigned char *crypt_session_encrypt(crypt_session_t *const s, const unsigned char *const m, unsigned long long mlen, unsigned long long *clen) {
+    unsigned char *c = (unsigned char *)malloc((mlen + crypto_aead_aegis256_ABYTES) * sizeof(unsigned char));
+
+    crypto_aead_aegis256_encrypt(c, clen, m, mlen, NULL, 0, NULL, s->nonce, s->tx);
+
+    return c;
+}
+
+unsigned char *crypt_session_decrypt(crypt_session_t *const s, const unsigned char *const c, unsigned long long clen, unsigned long long *mlen) {
+    unsigned char *m = (unsigned char *)malloc((clen - crypto_aead_aegis256_ABYTES) * sizeof(unsigned char));
+
+    if (crypto_aead_aegis256_decrypt(m, mlen, NULL, c, clen, NULL, 0, s->nonce, s->rx) != 0) {
+        free(m);
+        return NULL;
+    }
+
+    return m;
+}
+
+void crypt_session_destroy(crypt_session_t *const s) {
+    sodium_memzero(s->rx, CRYPT_SESS_KEY_LEN);
+    sodium_memzero(s->tx, CRYPT_SESS_KEY_LEN);
+    sodium_memzero(s->nonce, CRYPT_NONCE_LEN);
+    crypt_key_destroy(s->remote_key);
 }

src/crypt.h

@@ -6,9 +6,24 @@
 
 #include <sodium.h>
 
-#define CRYPT_PUBKEY_HEXSIZE (crypto_kx_PUBLICKEYBYTES + crypto_sign_PUBLICKEYBYTES) * 2
-#define CRYPT_SECKEY_HEXSIZE (crypto_kx_SECRETKEYBYTES + crypto_sign_SECRETKEYBYTES) * 2
+#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_NONCE_LEN crypto_aead_aegis256_NPUBBYTES
+#define CRYPT_NONCEHALF_LEN (CRYPT_NONCE_LEN/2)
+
+#define CRYPT_HELLO_LEN (CRYPT_PKEY_HEXLEN + CRYPT_SIGN_LEN + (CRYPT_NONCEHALF_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)
+
+// Stores the public and secret keys used in a key exchange and for signing.
 typedef struct crypt_key_t {
     unsigned char kx_pub[crypto_kx_PUBLICKEYBYTES];
     unsigned char kx_sec[crypto_kx_SECRETKEYBYTES];
@@ -17,22 +32,53 @@ typedef struct crypt_key_t {
     bool hasSecKey;
 } crypt_key_t;
 
-int crypt_key_gen(crypt_key_t *k);
-int crypt_key_from_hex(crypt_key_t *k, char phex[CRYPT_PUBKEY_HEXSIZE], char shex[CRYPT_SECKEY_HEXSIZE]);
-int crypt_key_from_hex_public(crypt_key_t *k, char phex[CRYPT_PUBKEY_HEXSIZE]);
+// 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, 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, const char phex[CRYPT_PKEY_HEXLEN]);
 
-void crypt_key_export_public(crypt_key_t *k, char hex[CRYPT_PUBKEY_HEXSIZE]);
-void crypt_key_export_secret(crypt_key_t *k, char hex[CRYPT_SECKEY_HEXSIZE]);
+// Securely erase the fields of a crypt_key_t struct.
+void crypt_key_destroy(crypt_key_t *const k);
 
-void crypt_store_public_key(crypt_key_t *k, FILE *out_file);
-void crypt_store_secret_key(crypt_key_t *k, FILE *out_file);
+// Export a public sign and key exchange keys as a hex string.
+int crypt_key_export_public(const crypt_key_t *const k, char hex[CRYPT_PKEY_HEXLEN]);
+// Export a secret sign and key exchange keys as a hex string.
+int crypt_key_export_secret(const crypt_key_t *const k, char hex[CRYPT_SKEY_HEXLEN]);
 
+// Load the sign and key exchange keys in a hex representaion from files
+// and initialise a crypt_key_t.
+int crypt_load_key(crypt_key_t *const k, FILE *const pub, FILE *const sec);
+// Store a hex representaion of the sign and key exchange keys into files
+// that are corresponding to a public and a secret parts.
+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 of CRYPT_SIGN_LEN long.
+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);
+// Combines own and remote halves of a nonce depending in a connection direction and returns it.
+// It will be of CRYPT_NONCE_LEN length.
+unsigned char *crypt_hello_get_nonce(const unsigned char *const own_hello, const unsigned char *const remote_hello, bool is_client);
+
+// Stores symmetric keys used for a data encryption in both directions
+// and a remote public key.
 typedef struct crypt_session_t {
-    unsigned char rx[crypto_kx_SESSIONKEYBYTES];
-    unsigned char tx[crypto_kx_SESSIONKEYBYTES];
+    unsigned char rx[CRYPT_SESS_KEY_LEN];
+    unsigned char tx[CRYPT_SESS_KEY_LEN];
+    unsigned char nonce[CRYPT_NONCE_LEN];
     crypt_key_t *remote_key;
 } crypt_session_t;
 
-int crypt_session_init(crypt_session_t *s, crypt_key_t *own, crypt_key_t *remote, bool is_client);
+// Derives the symmetric keys for a data encryption using own public and secret and remote's public keys.
+//
+// is_client should be set to true if you are the one establishing the connection.
+int crypt_session_init(crypt_session_t *const s, const crypt_key_t *const own, crypt_key_t *const remote, const unsigned char *const nonce, bool is_client);
+unsigned char *crypt_session_encrypt(crypt_session_t *const s, const unsigned char *const m, unsigned long long mlen, unsigned long long *clen);
+unsigned char *crypt_session_decrypt(crypt_session_t *const s, const unsigned char *const c, unsigned long long clen, unsigned long long *mlen);
+// Securely erase the fields of a crypt_session_t struct.
+void crypt_session_destroy(crypt_session_t *const s);
 
 #endif /* _CRYPT_H_ */

src/main.c

@@ -1,5 +1,5 @@
+#include <sodium/utils.h>
 #include <stdio.h>
-#include <stdint.h>
 #include <string.h>
 
 #include "audio.h"
@@ -20,25 +20,102 @@ int main(int argc, char **argv) {
         return -1;
     }
 
-    crypt_key_t own;
+    crypt_key_t own, remote;
 
     if (crypt_key_gen(&own) < 0) {
         fprintf(stderr, "Failed to generate the keys.");
         return -1;
     }
 
-    FILE *fp = fopen("own_pub_key", "w");
-    FILE *fs = fopen("own_sec_key", "w");
+    if (crypt_key_gen(&remote) < 0) {
+        fprintf(stderr, "Failed to generate the keys.");
+        return -1;
+    }
 
-    crypt_store_public_key(&own, fp);
-    crypt_store_secret_key(&own, fs);
+    unsigned char *oh = crypt_hello(&own);
+    unsigned char *rh = crypt_hello(&remote);
 
-    fclose(fp);
-    fclose(fs);
+    unsigned char *oc = NULL;
+    char *rmsg = NULL;
+    unsigned long long ocl = 0, rml = 0;
+
+    int rt = 0;
+    crypt_session_t os, rs;
+    unsigned char *nonce_own = NULL, *nonce_rem = NULL;
+
+    if (crypt_hello_verify(oh, &own) < 0) {
+        fprintf(stderr, "oh v fail");
+        rt = -1;
+        goto cleanup;
+    }
+
+    if (crypt_hello_verify(rh, &remote) < 0) {
+        fprintf(stderr, "rh v fail");
+        rt = -1;
+        goto cleanup;
+    }
+
+    nonce_own = crypt_hello_get_nonce(oh, rh, false);
+    nonce_rem = crypt_hello_get_nonce(rh, oh, true);
+
+    for (unsigned int i = 0; i < CRYPT_NONCE_LEN; ++i)
+        if (nonce_own[i] != nonce_rem[i]) {
+            fprintf(stderr, "A nonce mismatch occured.");
+            rt = -1;
+            goto cleanup;
+        }
+
+
+    if (crypt_session_init(&os, &own, &remote, nonce_own, true) < 0) {
+        rt = -1;
+        goto cleanup;
+    }
+
+    if (crypt_session_init(&rs, &remote, &own, nonce_rem, false) < 0) {
+        rt = -1;
+        goto cleanup;
+    }
+
+    char msg[] = "Hello!";
+    unsigned long long msglen = 6;
+
+    oc = crypt_session_encrypt(&os, (unsigned char *)msg, msglen, &ocl);
+
+    if (oc == NULL) {
+        fprintf(stderr, "oc is null");
+        rt = -1;
+        goto cleanup;
+    }
+
+    rmsg = (char *)crypt_session_decrypt(&rs, oc, ocl, &rml);
+
+    if (rmsg == NULL) {
+        rt = -1;
+        goto cleanup;
+    }
+
+    if (strcmp(msg, rmsg) != 0)
+        fprintf(stderr, "Yikes!");
+
+cleanup:
+    free(oh);
+    free(rh);
+
+    free(oc);
+    free(rmsg);
+
+    free(nonce_own);
+    free(nonce_rem);
+
+    crypt_key_destroy(&own);
+    crypt_key_destroy(&remote);
+
+    crypt_session_destroy(&os);
+    crypt_session_destroy(&rs);
 
     // audio_t aud;
 
-    // uint8_t buf[BUF_SIZE];
+    // unsigned char buf[BUF_SIZE];
     // memset(buf, 0, BUF_SIZE);
 
     // audio_init(&aud, CHANNELS, SAMPLE_RATE, FRAMES_PER_BUFFFER);
@@ -52,5 +129,5 @@ int main(int argc, char **argv) {
 
     // audio_destroy(&aud);
 
-    return 0;
+    return rt;
 }

src/net.c

@@ -1,6 +1,5 @@
 #include "net.h"
 
-#include <stdlib.h>
 #include <string.h>
 #include <unistd.h>