+ box_detached demo

demos/box.c

@@ -108,13 +108,13 @@ box(void)
     crypto_box_easy(ciphertext, message, message_len, nonce, alice_pk, bob_sk);
     ciphertext_len = crypto_box_MACBYTES + message_len;
 
-    /* send the ciphertext */
-    puts("Bob sends the ciphertext...\n");
+    /* send the nonce and the ciphertext */
+    puts("Bob sends the nonce and the ciphertext...\n");
     printf("Ciphertext len: %zu bytes - Original message length: %zu bytes\n",
            ciphertext_len, message_len);
     puts("Notice the prepended 16 byte authentication token\n");
     fputs("Nonce: ", stdout);
-    print_hex(ciphertext, ciphertext_len);
+    print_hex(nonce, nonce_len);
     putchar('\n');
     fputs("Ciphertext: ", stdout);
     print_hex(ciphertext, ciphertext_len);

demos/box_detached.c

@@ -0,0 +1,149 @@
+/*
+ * GraxRabble
+ * Demo programs for libsodium.
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <sodium.h> /* library header */
+
+#include "utils.h" /* utility functions shared by demos */
+
+/*
+ * Using public-key authenticated encryption, Bob can encrypt a
+ * confidential message specifically for Alice, using Alice's public
+ * key.
+ *
+ * Using Bob's public key, Alice can verify that the encrypted
+ * message was actually created by Bob and was not tampered with,
+ * before eventually decrypting it.
+ *
+ * Alice only needs Bob's public key, the nonce and the ciphertext.
+ * Bob should never ever share his secret key, even with Alice.
+ *
+ * And in order to send messages to Alice, Bob only needs Alice's
+ * public key. Alice should never ever share her secret key either,
+ * even with Bob.
+ *
+ * Alice can reply to Bob using the same system, without having to
+ * generate a distinct key pair.
+ *
+ * The nonce doesn't have to be confidential, but it should be used
+ * with just one invokation of crypto_box_open_easy() for a
+ * particular pair of public and secret keys.
+ *
+ * One easy way to generate a nonce is to use randombytes_buf(),
+ * considering the size of nonces the risk of any random collisions
+ * is negligible. For some applications, if you wish to use nonces to
+ * detect missing messages or to ignore replayed messages, it is also
+ * ok to use a simple incrementing counter as a nonce.
+ *
+ * When doing so you must ensure that the same value can never be
+ * re-used (for example you may have multiple threads or even hosts
+ * generating messages using the same key pairs).
+ *
+ * This system provides mutual authentication. However, a typical use
+ * case is to secure communications between a server, whose public
+ * key is known in advance, and clients connecting anonymously.
+ */
+static int
+box_detached(void)
+{
+    unsigned char bob_pk[crypto_box_PUBLICKEYBYTES]; /* Bob's public key */
+    unsigned char bob_sk[crypto_box_SECRETKEYBYTES]; /* Bob's secret key */
+
+    unsigned char alice_pk[crypto_box_PUBLICKEYBYTES]; /* Alice's public key */
+    unsigned char alice_sk[crypto_box_SECRETKEYBYTES]; /* Alice's secret key */
+
+    unsigned char nonce[crypto_box_NONCEBYTES];
+    unsigned char message[MAX_INPUT_SIZE];
+    unsigned char mac[crypto_box_MACBYTES];
+    unsigned char ciphertext[MAX_INPUT_SIZE];
+    size_t        message_len;
+    int           ret;
+
+    puts("Example: crypto_box_detached\n");
+
+    puts("Generating keypairs...\n");
+    crypto_box_keypair(bob_pk, bob_sk);     /* generate Bob's keys */
+    crypto_box_keypair(alice_pk, alice_sk); /* generate Alice's keys */
+
+    puts("Bob");
+    fputs("Public key: ", stdout);
+    print_hex(bob_pk, sizeof bob_pk);
+    putchar('\n');
+    fputs("Secret key: ", stdout);
+    print_hex(bob_sk, sizeof bob_sk);
+    putchar('\n');
+    putchar('\n');
+
+    puts("Alice");
+    fputs("Public key: ", stdout);
+    print_hex(alice_pk, sizeof alice_pk);
+    putchar('\n');
+    fputs("Secret key: ", stdout);
+    print_hex(alice_sk, sizeof alice_sk);
+    putchar('\n');
+    putchar('\n');
+
+    /* nonce must be unique per (key, message) - it can be public and deterministic */
+    puts("Generating nonce...");
+    randombytes_buf(nonce, sizeof nonce);
+    fputs("Nonce: ", stdout);
+    print_hex(nonce, sizeof nonce);
+    putchar('\n');
+    putchar('\n');
+
+    /* read input */
+    message_len = prompt_input("Enter a message > ",
+                               (char*)message, sizeof message);
+
+    print_hex(message, message_len);
+    putchar('\n');
+    putchar('\n');
+
+    /* encrypt and authenticate the message */
+    printf("Encrypting and authenticating with %s\n\n", crypto_box_primitive());
+    crypto_box_detached(ciphertext, mac, message, message_len, nonce,
+                        alice_pk, bob_sk);
+
+    /* send the nonce, the MAC and the ciphertext */
+    puts("Bob sends the nonce, the MAC and the ciphertext...\n");
+    fputs("Nonce: ", stdout);
+    print_hex(nonce, sizeof nonce);
+    putchar('\n');
+    fputs("MAC: ", stdout);
+    print_hex(mac, sizeof mac);
+    putchar('\n');
+    fputs("Ciphertext: ", stdout);
+    print_hex(ciphertext, message_len);
+    putchar('\n');
+    putchar('\n');
+
+    /* decrypt the message */
+    puts("Alice verifies the MAC and decrypts the ciphertext...");
+    ret = crypto_box_open_detached(message, ciphertext, mac, message_len, nonce,
+                                   bob_pk, alice_sk);
+    print_hex(message, message_len);
+    putchar('\n');
+
+    print_verification(ret);
+    if (ret == 0)
+        printf("Plaintext: %s\n\n", message);
+
+    sodium_memzero(bob_sk, sizeof bob_sk); /* wipe sensitive data */
+    sodium_memzero(alice_sk, sizeof alice_sk);
+    sodium_memzero(message, sizeof message);
+    sodium_memzero(ciphertext, sizeof ciphertext);
+
+    return ret;
+}
+
+int
+main(void)
+{
+    init();
+
+    return box_detached() != 0;
+}