/* Provenance: openssl/openssl sm2_plaintext_size (vuln).
 * repo: openssl/openssl
 * commit: 8c74c9d1ade0fbdab5b815ddb747351b8b839641
 * parent: 8c74c9d1ade0fbdab5b815ddb747351b8b839641
 * commit_url: https://github.com/openssl/openssl/commit/59f5e75f3bced8fc0e130d72a3f582cf7b480b46
 * cve: CVE-2021-3711
 * license: OpenSSL License
 * function: sm2_plaintext_size
 * relpath: crypto/sm2/sm2_crypt.c
 */

int sm2_plaintext_size(const EC_KEY *key, const EVP_MD *digest, size_t msg_len,
                       size_t *pt_size)
{
    const size_t field_size = ec_field_size(EC_KEY_get0_group(key));
    const int md_size = EVP_MD_size(digest);
    size_t overhead;

    if (md_size < 0) {
        SM2err(SM2_F_SM2_PLAINTEXT_SIZE, SM2_R_INVALID_DIGEST);
        return 0;
    }
    if (field_size == 0) {
        SM2err(SM2_F_SM2_PLAINTEXT_SIZE, SM2_R_INVALID_FIELD);
        return 0;
    }

    overhead = 10 + 2 * field_size + (size_t)md_size;
    if (msg_len <= overhead) {
        SM2err(SM2_F_SM2_PLAINTEXT_SIZE, SM2_R_INVALID_ENCODING);
        return 0;
    }

    *pt_size = msg_len - overhead;
    return 1;
}