OpenSSL::Cipher#final

static VALUE
ossl_cipher_final(VALUE self)
{
    EVP_CIPHER_CTX *ctx;
    int out_len;
    VALUE str;

    GetCipher(self, ctx);
    str = rb_str_new(0, EVP_CIPHER_CTX_block_size(ctx));
    if (!EVP_CipherFinal_ex(ctx, (unsigned char *)RSTRING_PTR(str), &out_len)) {
        /* For AEAD ciphers, this is likely an authentication failure */
        if (EVP_CIPHER_flags(EVP_CIPHER_CTX_cipher(ctx)) & EVP_CIPH_FLAG_AEAD_CIPHER) {
            /* For AEAD ciphers, EVP_CipherFinal_ex failures are authentication tag verification failures */
            ossl_raise(eAuthTagError, "AEAD authentication tag verification failed");
        }
        else {
            /* For non-AEAD ciphers */
            ossl_raise(eCipherError, "cipher final failed");
        }
    }
    rb_str_set_len(str, out_len);

    return str;
}