Rust

Decrypt File in Chunks using 256-bit AES

See more Encryption Examples

Shows how to decrypt a file chunk-by-chunk using FirstChunk/LastChunk properties and accumulate the results in memory with a Chilkat BinData object. Rust

// This example assumes the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// This example decrypts the file previously encrypted in this example:
// Encrypt File in Chunks using AES CBC

let crypt = chilkat::Crypt2::new();

crypt.set_crypt_algorithm("aes");
crypt.set_cipher_mode("cbc");
crypt.set_key_length(256);

crypt.set_encoded_key("000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F", "hex");
crypt.set_encoded_iv("000102030405060708090A0B0C0D0E0F", "hex");

let file_to_decrypt = "c:/temp/qa_output/hamlet.enc".to_string();
let fac_in = chilkat::FileAccess::new();
if fac_in.open_for_read(&file_to_decrypt).is_err() {
    println!("Failed to open file to be decrytped.");
    return;
}

// Let's decrypt in 32000 byte chunks.
let chunk_size = 32000;
let num_chunks = fac_in.get_num_blocks(chunk_size);

crypt.set_first_chunk(true);
crypt.set_last_chunk(false);

let bd = chilkat::BinData::new();
let bd_decrypted = chilkat::BinData::new();

let mut i = 0;
while i < num_chunks {
    i = i + 1;
    if i == num_chunks {
        crypt.set_last_chunk(true);
    }

    // Read the next chunk from the file.
    // The last chunk will be whatever amount remains in the file..
    let _ = bd.clear();
    let _ = fac_in.file_read_bd(chunk_size, &bd);

    // Decrypt this chunk.
    let _ = crypt.decrypt_bd(&bd);
    // Accumulate the decrypted chunks.
    let _ = bd_decrypted.append_bd(&bd);

    crypt.set_first_chunk(false);
}

// Make sure both FirstChunk and LastChunk are restored to true after
// encrypting or decrypting in chunks.  Otherwise subsequent encryptions/decryptions
// will produce unexpected results.
crypt.set_first_chunk(true);
crypt.set_last_chunk(true);

fac_in.file_close();

// The fully decrypted file is contained in bdDecrypted.
// You can save to a file if desired, or use the decrypted data in your application directly from bdDecrypted.
let _ = bd_decrypted.write_file("c:/temp/qa_output/hamlet_decrypted.xml");