EVP_CipherInit(&ctx, NULL, NULL, p, 0);
EVP_Cipher(&ctx, p + ivlen, p + ivlen, ep - (p + ivlen));
EVP_CIPHER_CTX_cleanup(&ctx);
EVP_CipherInit(&ctx, NULL, NULL, p, 0);
EVP_Cipher(&ctx, p + ivlen, p + ivlen, ep - (p + ivlen));
EVP_CIPHER_CTX_cleanup(&ctx);