rust-bottle 0.2.3

//! TPM/HSM support for rust-bottle.
//!
//! This module provides an interface for using Trusted Platform Modules (TPM)
//! and Hardware Security Modules (HSM) with rust-bottle's ECDH operations.
//!
//! # Example
//!
//! ```rust,no_run
//! use rust_bottle::tpm::ECDHHandler;
//! use rust_bottle::ecdh::ecdh_encrypt_with_handler;
//! use rand::rngs::OsRng;
//!
//! // Create a TPM handler (implementation depends on your TPM library)
//! // let tpm_handler = TpmHandler::new()?;
//!
//! // Use it for encryption
//! // let ciphertext = ecdh_encrypt_with_handler(
//! //     &mut OsRng,
//! //     b"Secret message",
//! //     &public_key_bytes,
//! //     Some(&tpm_handler),
//! // )?;
//! ```

use crate::errors::{BottleError, Result};

/// Trait for ECDH operations that can be performed by TPM/HSM backends.
///
/// This trait allows custom hardware backends (TPM, HSM, etc.) to provide
/// ECDH key exchange operations. Implementations should handle the key exchange
/// using the hardware module and return the shared secret.
///
/// This is similar to gobottle's `ECDHHandler` interface.
///
/// # Example
///
/// ```rust,no_run
/// use rust_bottle::tpm::ECDHHandler;
/// use rust_bottle::errors::Result;
///
/// struct MyTpmHandler {
///     // TPM-specific fields
/// }
///
/// impl ECDHHandler for MyTpmHandler {
///     fn public_key(&self) -> Result<Vec<u8>> {
///         // Return the public key from TPM
///         Ok(vec![])
///     }
///
///     fn ecdh(&self, peer_public_key: &[u8]) -> Result<Vec<u8>> {
///         // Perform ECDH using TPM
///         Ok(vec![])
///     }
/// }
/// ```
pub trait ECDHHandler {
    /// Get the public key associated with this handler.
    ///
    /// The public key should be in the same format as the corresponding
    /// software key type (e.g., 32 bytes for X25519, 65 bytes for P-256).
    ///
    /// # Returns
    ///
    /// * `Ok(Vec<u8>)` - The public key bytes
    /// * `Err(BottleError)` - If the key cannot be retrieved
    fn public_key(&self) -> Result<Vec<u8>>;

    /// Perform ECDH key exchange with a peer's public key.
    ///
    /// This function computes the shared secret using the handler's private
    /// key (stored in TPM/HSM) and the peer's public key.
    ///
    /// # Arguments
    ///
    /// * `peer_public_key` - The peer's public key bytes
    ///
    /// # Returns
    ///
    /// * `Ok(Vec<u8>)` - The shared secret bytes
    /// * `Err(BottleError)` - If the ECDH operation fails
    fn ecdh(&self, peer_public_key: &[u8]) -> Result<Vec<u8>>;
}

#[cfg(feature = "tpm")]
mod tpm_impl {
    use super::*;

    /// TPM handler implementation using tss-esapi or similar.
    ///
    /// This is a placeholder implementation. Users should implement
    /// `ECDHHandler` for their specific TPM library.
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// use rust_bottle::tpm::{ECDHHandler, TpmHandler};
    ///
    /// // Initialize TPM handler
    /// // let handler = TpmHandler::new()?;
    ///
    /// // Get public key
    /// // let pub_key = handler.public_key()?;
    ///
    /// // Perform ECDH
    /// // let shared_secret = handler.ecdh(&peer_pub_key)?;
    /// ```
    pub struct TpmHandler {
        // TPM-specific fields would go here
        // This is a placeholder structure
    }

    impl TpmHandler {
        /// Create a new TPM handler.
        ///
        /// This function initializes a connection to the TPM and loads
        /// or creates a key for ECDH operations.
        ///
        /// # Returns
        ///
        /// * `Ok(TpmHandler)` - A new TPM handler
        /// * `Err(BottleError)` - If TPM initialization fails
        pub fn new() -> Result<Self> {
            // Placeholder implementation
            // In a real implementation, this would:
            // 1. Connect to the TPM
            // 2. Load or create an ECDH key
            // 3. Return the handler
            Err(BottleError::UnsupportedAlgorithm)
        }
    }

    impl ECDHHandler for TpmHandler {
        fn public_key(&self) -> Result<Vec<u8>> {
            // Placeholder implementation
            // In a real implementation, this would retrieve the public key from TPM
            Err(BottleError::UnsupportedAlgorithm)
        }

        fn ecdh(&self, _peer_public_key: &[u8]) -> Result<Vec<u8>> {
            // Placeholder implementation
            // In a real implementation, this would:
            // 1. Parse the peer's public key
            // 2. Use TPM to perform ECDH
            // 3. Return the shared secret
            Err(BottleError::UnsupportedAlgorithm)
        }
    }
}

#[cfg(feature = "tpm")]
pub use tpm_impl::TpmHandler;