Key Idea
Bitcoin blocks are timestamped and generated approximately every 10 minutes. These timestamps, along with data from the block (e.g., block hash), can act as a dynamic, time-dependent key or seed in a cryptographic scheme.
How It Works
Block Hash as Key Material: Use the hash of a specific Bitcoin block as part of the key material. For example, block N’s hash (or a portion of it) could serve as the encryption key for data until block N+1 is mined.
Encryption Process:
- Obtain the latest block hash (or a specific part of the block data)
- Use a cryptographic function like AES to encrypt data with the block hash as the key
Decryption Process:
- The recipient waits for the corresponding block to be mined or refers to the same block that was used for encryption
- They retrieve the block hash from a reliable source (e.g., Bitcoin network or block explorer)
- Decrypt the data using the block hash as the key
Time-Locking: By specifying which block hash to use, you can enforce a time-locking mechanism. For example, “This message can only be decrypted after block N+2” requires the recipient to wait until that block is mined.
Algorithm
- At encryption time, take the current latest block_id (BID) and its blockhash - this is the root of the encryption
- State how much time you want to lock the message for (e.g., 20 minutes)
- Divide the time by the average new blocktime to get the number of block hashes that need to be collected between BID and THEN
- n is the number of consecutive individual blockhashes that needs to be collected, starting from the current BID
- Encrypt the message with the current blockhash and a private key
- To decrypt the message, the hash of BID + n consecutive hashes must be entered to reveal the message
Implementation in Rust
use sha2::{Sha256, Digest};
use aes_gcm::aead::{Aead, KeyInit, OsRng};
use aes_gcm::{Aes256Gcm, Nonce};
fn encrypt_with_block_hash(data: &[u8], block_hash: &str) -> Vec<u8> {
// Hash the block hash to derive a symmetric key
let mut hasher = Sha256::new();
hasher.update(block_hash.as_bytes());
let key = hasher.finalize();
// Use AES-GCM encryption
let cipher = Aes256Gcm::new_from_slice(&key).expect("Key generation failed");
let nonce = Nonce::from_slice(b"unique nonce"); // Use a secure method to generate this in production
cipher.encrypt(nonce, data).expect("Encryption failed")
}
Decrypt:
fn decrypt_with_block_hash(encrypted_data: &[u8], block_hash: &str) -> Vec<u8> {
let mut hasher = Sha256::new();
hasher.update(block_hash.as_bytes());
let key = hasher.finalize();
let cipher = Aes256Gcm::new_from_slice(&key).expect("Key generation failed");
let nonce = Nonce::from_slice(b"unique nonce"); // Same nonce as used during encryption
cipher.decrypt(nonce, encrypted_data).expect("Decryption failed")
}
Use Cases
Block Hash Retrieval: Use a Bitcoin RPC client or a block explorer API to get the latest block hash.
Time-Locking Messages: Encrypt messages that can only be decrypted after a specific block is mined.
Proof of Time: The encryption key’s dependency on the block hash proves that the data was encrypted at a specific point in the blockchain timeline.
Dependencies
[dependencies]
aes-gcm = "0.10" # AES-GCM for encryption
aes-gcm-siv = "0.10"
rand = "0.8" # For generating random initialization vectors (IVs)
clap = "4.0" # Command-line argument parsing
use aes_gcm::{Aes256Gcm, KeyInit, Nonce}; // Or `Aes128Gcm`
use aes_gcm::aead::{Aead, OsRng}; // Random number generator
use clap::{Parser, Subcommand};
use std::fs;
Command-Line Interface
CLI Structure:
/// Struct for command-line argument parsing
#[derive(Parser)]
#[command(name = "File Encryptor")]
#[command(about = "Encrypt and decrypt files using a password", long_about = None)]
struct Cli {
#[command(subcommand)]
operation: Operation,
}
#[derive(Subcommand)]
enum Operation {
Encrypt {
#[arg(short, long)]
input: String,
#[arg(short, long)]
output: String,
#[arg(short, long)]
password: String,
},
Decrypt {
#[arg(short, long)]
input: String,
#[arg(short, long)]
output: String,
#[arg(short, long)]
password: String,
},
}
fn derive_key(password: &str) -> [u8; 32] {
let mut hasher = sha2::Sha256::new();
hasher.update(password.as_bytes());
let result = hasher.finalize();
let mut key = [0u8; 32];
key.copy_from_slice(&result[..32]);
key
}
fn encrypt_file(input_path: &str, output_path: &str, password: &str) -> Result<(), Box<dyn std::error::Error>> {
let plaintext = fs::read(input_path)?;
let key = derive_key(password);
let cipher = Aes256Gcm::new_from_slice(&key).expect("Invalid key length");
let nonce = aes_gcm::Nonce::from_slice(&rand::random::<[u8; 12]>());
let ciphertext = cipher.encrypt(nonce, plaintext.as_ref())
.expect("Encryption failed");
let mut output_data = nonce.to_vec();
output_data.extend_from_slice(&ciphertext);
fs::write(output_path, output_data)?;
println!("File encrypted successfully!");
Ok(())
}
fn decrypt_file(input_path: &str, output_path: &str, password: &str) -> Result<(), Box<dyn std::error::Error>> {
let input_data = fs::read(input_path)?;
let (nonce, ciphertext) = input_data.split_at(12);
let key = derive_key(password);
let cipher = Aes256Gcm::new_from_slice(&key).expect("Invalid key length");
let plaintext = cipher.decrypt(Nonce::from_slice(nonce), ciphertext)
.expect("Decryption failed: Incorrect password or corrupted file");
fs::write(output_path, plaintext)?;
println!("File decrypted successfully!");
Ok(())
}
fn main() {
let cli = Cli::parse();
match cli.operation {
Operation::Encrypt { input, output, password } => {
if let Err(e) = encrypt_file(&input, &output, &password) {
eprintln!("Error during encryption: {}", e);
}
}
Operation::Decrypt { input, output, password } => {
if let Err(e) = decrypt_file(&input, &output, &password) {
eprintln!("Error during decryption: {}", e);
}
}
}
}
How The Encryption Works
Key Derivation:
- A SHA-256 hash of the password is used as the encryption key
- This ensures consistent and strong key generation
Nonce:
- A 12-byte random nonce is generated for each encryption
- It is prepended to the ciphertext and stored in the output file
Encrypt/Decrypt Workflow:
- During encryption, the file content is read, encrypted with AES-GCM, and written along with the nonce to the output file
- During decryption, the nonce is extracted, and the ciphertext is decrypted
Usage
Encrypt a file:
cargo run -- encrypt -i input.txt -o encrypted.bin -p mypassword
Decrypt a file:
cargo run -- decrypt -i encrypted.bin -o decrypted.txt -p mypassword
Security Notes
Password Strength: Ensure the password is strong, as it directly affects the security of the encryption.
Nonce Management: The nonce is unique per file and stored with the ciphertext. Reusing nonces with the same key would compromise security.
Error Handling: The program gracefully handles errors, like incorrect passwords or corrupted files, and informs the user.
This program is secure and flexible for encrypting and decrypting files with a password. You can extend it further by adding support for key files or integrating it with a secure storage system.