gcry.cc

#include "gcry.hh"

void xerr(const char* msg)
{
    fprintf(stderr, "%s\n", msg);
    exit(1);
}

void gcrypt_init()
{
    /* Version check should be the very first call because it
       makes sure that important subsystems are intialized. */
    if (!gcry_check_version (GCRYPT_VERSION))
    {
        xerr("gcrypt: library version mismatch");
    }

    gcry_error_t err = 0;

    /* We don't want to see any warnings, e.g. because we have not yet
       parsed program options which might be used to suppress such
       warnings. */
    err = gcry_control (GCRYCTL_SUSPEND_SECMEM_WARN);

    /* ... If required, other initialization goes here.  Note that the
       process might still be running with increased privileges and that
       the secure memory has not been intialized.  */

    /* Allocate a pool of 16k secure memory.  This make the secure memory
       available and also drops privileges where needed.  */
    err |= gcry_control (GCRYCTL_INIT_SECMEM, 16384, 0);

    /* It is now okay to let Libgcrypt complain when there was/is
       a problem with the secure memory. */
    err |= gcry_control (GCRYCTL_RESUME_SECMEM_WARN);

    /* ... If required, other initialization goes here.  */

    /* Tell Libgcrypt that initialization has completed. */
    err |= gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0);

    if (err) {
        xerr("gcrypt: failed initialization");
    }
}

size_t get_keypair_size(int nbits)
{
    size_t aes_blklen = gcry_cipher_get_algo_blklen(GCRY_CIPHER_AES128);
    return nbits * aes_blklen;
}

void get_aes_ctx(gcry_cipher_hd_t* aes_hd)
{
    const size_t keylen = 16;
    char passwd_hash[keylen];

    char* passwd = getpass("Keypair Password: ");
    size_t pass_len = passwd ? strlen(passwd) : 0;
    if (pass_len == 0) {
        xerr("getpass: not a valid password");
    }

    int err = gcry_cipher_open(aes_hd, GCRY_CIPHER_AES128, 
                               GCRY_CIPHER_MODE_CFB, 0);
    if (err) {
        xerr("gcrypt: failed to create aes handle");
    }

    gcry_md_hash_buffer(GCRY_MD_MD5, (void*) &passwd_hash, 
                        (const void*) passwd, pass_len);

    err = gcry_cipher_setkey(*aes_hd, (const void*) &passwd_hash, keylen);
    if (err) {
        xerr("gcrypt: could not set cipher key");
    }

    err = gcry_cipher_setiv(*aes_hd, (const void*) &passwd_hash, keylen);
    if (err) {
        xerr("gcrypt: could not set cipher initialization vector");
    }
}