source: creddy/generate.c @ 5a72d21

#include <fcntl.h>

#include <credentials/keys/private_key.h>

#include "creddy.h"

#define KEY_SUFFIX  "_private.der"
#define CERT_SUFFIX "_ID.pem"

static private_key_t *_generate_key(char *filename);
static void _generate_cert(char *filename, private_key_t *private, char *cn, int validity);

void generate_main(options_t *opts) {
    int ret;
    chunk_t encoding;
    char *cn = opts->cn, *filename;
    int cn_len;
    private_key_t *key;

    if (cn == NULL)
        usage(opts);

    if (!clean_name(cn)) {
        printf("Invalid CN: must start with a letter and be alphanumeric\n");
        usage(opts);
    }
    if (opts->validity <= 0) {
        printf("Validity must be >= 1 day\n");
        usage(opts);
    }

    cn_len = strlen(cn);

    // key output filename: "${cn}_private.der"
    filename = xmalloc(cn_len + sizeof(KEY_SUFFIX));
    memcpy(filename, cn, cn_len);

    memcpy(filename + cn_len, KEY_SUFFIX, sizeof(KEY_SUFFIX));
    key = _generate_key(filename);

    // cert filename: ${cn}_ID.pem
    memcpy(filename +cn_len, CERT_SUFFIX, sizeof(CERT_SUFFIX));
    _generate_cert(filename, key, cn, opts->validity);

    free(filename);
    DESTROY_IF(key);
}

static private_key_t *_generate_key(char *filename) {
    private_key_t *key;
    int ret;
    chunk_t encoding;

    printf("Generating key, this will take a while. Create entropy!\n");
    printf("    - move the mouse\n");
    printf("    - generate disk activity (run find)\n");

    // generate the key
    key = lib->creds->create(
        lib->creds,
        CRED_PRIVATE_KEY, KEY_RSA,
        BUILD_KEY_SIZE, 2048,
        BUILD_END
    );
    if (key == NULL)
        errx(1, "Key generation failed");

    // get the key encoding
    ret = key->get_encoding(key, KEY_PRIV_ASN1_DER, &encoding);
    if (!ret)
        errx(1, "Couldn't encode private key");

    // write it to a file (with mode 600)
    int fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, 0600);
    if (fd < 0)
        err(1, "Couldn't open %s for writing private key", filename);

    ret = write(fd, encoding.ptr, encoding.len);
    if (ret < encoding.len)
        errx(1, "Couldn't write all the bytes of the private key");

    close(fd);

    free(encoding.ptr);

    return key;
}

static char *_create_dn(char *cn) {

#define DN "cn="

    char *dn = xmalloc(sizeof(DN) + strlen(cn));
    memcpy(dn, DN, sizeof(DN));
    strcat(dn, cn);

    return dn;
}

#define BYTES_PER_LINE 64

// thx libstrongswan
static void _encode_base64(char *filename, chunk_t encoding) {
    int start;

    chunk_t b64 = chunk_to_base64(encoding, NULL);

    FILE *out = fopen(filename, "w");
    if (out == NULL)
        err(1, "couldn't open %s for writing", filename);

    fprintf(out, "-----BEGIN CERTIFICATE-----\n");

    for (start = 0; start < b64.len; start += BYTES_PER_LINE) {
        int left = b64.len - start;
        int len = left < BYTES_PER_LINE ? left : BYTES_PER_LINE;
        fwrite(b64.ptr + start, len, 1, out);
        fprintf(out, "\n");
    }

    fprintf(out, "-----END CERTIFICATE-----\n");
    fclose(out);

    free(b64.ptr);
}

static void _generate_cert(char *filename, private_key_t *private, char *cn, int validity) {
    // build the DN
    char *dn_string = _create_dn(cn);
    identification_t *id = identification_create_from_string(dn_string);
    if (id == NULL)
        errx(1, "couldn't create ID from DN %s", dn_string);
    free(dn_string);

    // get the public key
    public_key_t *public = private->get_public_key(private);
    if (public == NULL)
        errx(1, "couldn't get public key from private key");

    // create a serial (stolen from strongswan pki)
    rng_t *rng = lib->crypto->create_rng(lib->crypto, RNG_WEAK);
    if (!rng)
        errx(1, "no random number generator");

    // random serial
    chunk_t serial = generate_serial();

    // validity period
    time_t not_before = time(NULL);
    time_t not_after = not_before + validity * 24 * 60 * 60;

    // create!
    certificate_t *cert = lib->creds->create(lib->creds,
        CRED_CERTIFICATE, CERT_X509,
        BUILD_SIGNING_KEY, private,
        BUILD_PUBLIC_KEY, public,
        BUILD_SUBJECT, id,
        BUILD_NOT_BEFORE_TIME, not_before,
        BUILD_NOT_AFTER_TIME, not_after,
        BUILD_SERIAL, serial,
        BUILD_DIGEST_ALG, HASH_SHA1,
        BUILD_X509_FLAG, X509_CA,
        BUILD_PATHLEN, X509_NO_PATH_LEN_CONSTRAINT,
        BUILD_END
    );
    if (cert == NULL)
        errx(1, "couldn't build cert :(");

    chunk_t encoding = cert->get_encoding(cert);

    // sigh
    _encode_base64(filename, encoding);

    DESTROY_IF(id);
    DESTROY_IF(cert);
    DESTROY_IF(public);
    free(encoding.ptr);
    free(serial.ptr);
}

chunk_t generate_serial() {
    chunk_t serial = chunk_empty;

    // create a serial (stolen from strongswan pki)
    rng_t *rng = lib->crypto->create_rng(lib->crypto, RNG_WEAK);
    if (!rng)
        errx(1, "no random number generator");

    rng->allocate_bytes(rng, 8, &serial);
    while (serial.ptr[0] == 0)
        // don't get leading 0's
        rng->get_bytes(rng, 1, serial.ptr);
    rng->destroy(rng);

    return serial;
}