diff --git a/demos/box.c b/demos/box.c index 7e33d9e4..09693f42 100644 --- a/demos/box.c +++ b/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); diff --git a/demos/box_detached.c b/demos/box_detached.c new file mode 100644 index 00000000..c37307cb --- /dev/null +++ b/demos/box_detached.c @@ -0,0 +1,149 @@ +/* + * GraxRabble + * Demo programs for libsodium. + */ +#include +#include +#include + +#include /* 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; +}