genkey.c

// FOR EDUCATIONAL PURPOSES ONLY
//
#include <stdio.h>
#include <sodium.h>

#define B64VARIANT sodium_base64_VARIANT_ORIGINAL_NO_PADDING

int main() {
    if (sodium_init() == -1) {
        return 3;
    }
    unsigned char pk[crypto_box_PUBLICKEYBYTES];
    unsigned char sk[crypto_box_SECRETKEYBYTES];
    crypto_box_keypair(pk, sk);
    char str_pk[sodium_base64_ENCODED_LEN(crypto_box_PUBLICKEYBYTES, B64VARIANT)];
    char str_sk[sodium_base64_ENCODED_LEN(crypto_box_SECRETKEYBYTES, B64VARIANT)];
    sodium_bin2base64(str_pk, sizeof(str_pk), pk, sizeof(pk), B64VARIANT);
    sodium_bin2base64(str_sk, sizeof(str_sk), sk, sizeof(sk), B64VARIANT);
    printf("PK=\t%s\n", str_pk);
    printf("SK=\t%s\n", str_sk);
}

Makefile

CCOPTS= -Os -s
CCOPTS+=$(shell pkg-config --cflags --static libsodium)
LDFLAGS= -static
LDFLAGS+=$(shell pkg-config --libs --static libsodium)

all: secsend genkey

%: %.c
	$(CC) -o "$@" $< $(CCOPTS) $(LDFLAGS)

clean:
	rm -f secsend genkey

.PHONY: clean

secsend.c

// FOR EDUCATIONAL PURPOSES ONLY
//
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sodium.h>

#define B64VARIANT sodium_base64_VARIANT_ORIGINAL_NO_PADDING
#define PKLEN (sodium_base64_ENCODED_LEN(crypto_box_PUBLICKEYBYTES, B64VARIANT) - 1)

#define INITIAL_BUFFER 4096
#define READ_CHUNK 4096
#define BUFFER_STEP 4096

void read_stdin(void **buf, size_t *size) {
    size_t bytes_read = 0;
    char *indata = malloc(INITIAL_BUFFER);
    char *inptr = indata;
    if (indata == NULL) {
        *size = 0;
        *buf = NULL;
        return;
    }
    size_t cur_buf_size = INITIAL_BUFFER;
    
    for (;;) {
        // Adjust read buffer pointer and read another portion of data
        inptr = indata + bytes_read;
        size_t chunk_read = fread(inptr, 1, READ_CHUNK, stdin);
        bytes_read += chunk_read;
        if (feof(stdin) || ferror(stdin)) break;

        // Expand buffer if needed
        if (cur_buf_size - bytes_read < READ_CHUNK) {
            void *new_buf = realloc(indata, cur_buf_size + BUFFER_STEP);
            if (new_buf == NULL) {
                free(indata);
                *size = 0;
                *buf = NULL;
                return;
            }
            indata = new_buf;
            cur_buf_size += BUFFER_STEP;
        }
    }
    *size = bytes_read;
    *buf = indata;
}

int send_data(void *data, size_t datalen, const char *host, uint16_t port) {
    int sockfd;
    struct sockaddr_in servaddr, cli;
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd == -1) {
        return 1;
    }
    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = inet_addr(host);
    if (servaddr.sin_addr.s_addr == INADDR_NONE) return 1;
    servaddr.sin_port = htons(port);

    if (connect(sockfd, (const struct sockaddr *)&servaddr, sizeof(servaddr)) != 0) {
        return 1;
    }

    write(sockfd, data, datalen);
    close(sockfd);
}

void usage() {
    fprintf(stderr, "\nUsage:\n\n");
    fprintf(stderr, "secsend <public key in B64 w/o padding> <host> <port>\n");
}

int main(int argc, char *argv[])
{
    if (argc != 4) {
        fprintf(stderr, "Bad argument count.\n");
        usage();
        return 2;
    }
    if (sodium_init() == -1) {
        return 3;
    }

    if (strlen(argv[1]) != PKLEN) {
        fprintf(stderr, "Bad key string length (%d).\n", strlen(argv[1]));
        usage();
        return 2;
    }

    // Parse PK
    unsigned char pk[crypto_box_PUBLICKEYBYTES];
    size_t decoded;
    if (sodium_base642bin(pk, sizeof(pk),
                          argv[1], strlen(argv[1]),
                          NULL, &decoded, NULL, B64VARIANT) == 0) {
        if (decoded != crypto_box_PUBLICKEYBYTES) {
            fprintf(stderr, "Bad length of parsed key material (%d).\n", decoded);
            usage();
            return 2;
        }
    } else {
        fprintf(stderr, "B64 parse of key failed.\n");
        usage();
        return 2;
    }

    char *host = argv[2];

    // Parse port number
    long int port = strtol(argv[3], NULL, 10);
    if (port <= 0 || port > 65535) {
        fprintf(stderr, "Bad port number.");
        usage();
        return 2;
    }

    // Read data from stdin
    size_t bytes_read;
    void *data_read;
    read_stdin(&data_read, &bytes_read);
    if (!bytes_read || !data_read) {
        return 4;
    }

    // Prepare buffer for ciphertext
    void *ciphertext = malloc(bytes_read + crypto_box_SEALBYTES);
    if (!ciphertext) {
        free(data_read);
        return 1;
    }

    crypto_box_seal(ciphertext, data_read, bytes_read, pk);
    free(data_read);
    if (send_data(ciphertext, bytes_read + crypto_box_SEALBYTES, host, port)) {
        free(ciphertext);
        return 10;
    }
    free(ciphertext);
    return 0;
}