bc-components 0.18.2

use anyhow::{ bail, Error, Result };
use bc_ur::prelude::*;
use crate::{
    tags,
    Digest,
    EncapsulationPublicKey,
    Encrypter,
    Reference,
    ReferenceProvider,
    Signature,
    SigningPublicKey,
    Verifier,
};

/// A container for an entity's public cryptographic keys.
///
/// `PublicKeys` combines a verification key for checking digital signatures with an
/// encapsulation key for encrypting messages, providing a complete public key
/// package for secure communication with an entity.
///
/// This type is designed to be freely shared across networks and systems, allowing
/// others to securely communicate with the key owner, who holds the corresponding
/// `PrivateKeys` instance.
///
/// # Components
///
/// * `signing_public_key` - A public key used for verifying digital signatures.
///   Can verify signatures created by the corresponding private key, which may be
///   Schnorr, ECDSA, Ed25519, or SSH-based.
///
/// * `encapsulation_public_key` - A public key used for encrypting messages that
///   can only be decrypted by the holder of the corresponding private key.
///   Can be X25519 or ML-KEM based.
///
/// # Use Cases
///
/// * Verifying the authenticity of signed messages or content
/// * Encrypting data for secure transmission to the key owner
/// * Identity verification in distributed systems
/// * Establishing secure communication channels
///
/// # Examples
///
/// ```
/// use bc_components::{keypair, EncapsulationPublicKey};
///
/// // Generate a key pair
/// let (private_keys, public_keys) = keypair();
///
/// // Get the encapsulation public key
/// let enc_pub_key = public_keys.enapsulation_public_key();
///
/// // The public key can be used for key encapsulation
/// // The resulting shared secret is only accessible to the 
/// // holder of the corresponding private key
/// ```
#[derive(Clone, PartialEq, Eq, Debug, Hash)]
pub struct PublicKeys {
    signing_public_key: SigningPublicKey,
    encapsulation_public_key: EncapsulationPublicKey,
}

impl PublicKeys {
    /// Restores a `PublicKeys` from a `SigningPublicKey` and an `EncapsulationPublicKey`.
    pub fn new(
        signing_public_key: SigningPublicKey,
        encapsulation_public_key: EncapsulationPublicKey
    ) -> Self {
        Self {
            signing_public_key,
            encapsulation_public_key,
        }
    }

    /// Returns the `SigningPublicKey` of this `PublicKeys`.
    pub fn signing_public_key(&self) -> &SigningPublicKey {
        &self.signing_public_key
    }

    /// Returns the `EncapsulationPublicKey` of this `PublicKeys`.
    pub fn enapsulation_public_key(&self) -> &EncapsulationPublicKey {
        &self.encapsulation_public_key
    }
}

/// A trait for types that can provide a complete set of public cryptographic keys.
///
/// Types implementing this trait can be used as a source of `PublicKeys`,
/// which contain both verification and encryption public keys. This trait is
/// particularly useful for key management systems, wallets, identity systems,
/// or any component that needs to provide public keys for cryptographic operations.
///
/// # Examples
///
/// ```
/// use bc_components::{PrivateKeyBase, PublicKeysProvider};
///
/// // Create a provider of public keys (in this case, a private key base
/// // that can derive the corresponding public keys)
/// let key_base = PrivateKeyBase::new();
///
/// // Get the public keys from the provider
/// let public_keys = key_base.public_keys();
/// 
/// // These public keys can be shared with others for secure communication
/// ```
pub trait PublicKeysProvider {
    /// Returns a complete set of public keys for cryptographic operations.
    ///
    /// The returned `PublicKeys` instance contains both verification and encryption
    /// public keys that can be used by other parties to securely communicate with
    /// the key owner.
    ///
    /// # Returns
    ///
    /// A `PublicKeys` instance containing the complete set of public keys.
    fn public_keys(&self) -> PublicKeys;
}

impl PublicKeysProvider for PublicKeys {
    fn public_keys(&self) -> PublicKeys {
        self.clone()
    }
}

impl ReferenceProvider for PublicKeys {
    fn reference(&self) -> Reference {
        Reference::from_digest(Digest::from_image(self.tagged_cbor().to_cbor_data()))
    }
}

impl AsRef<PublicKeys> for PublicKeys {
    fn as_ref(&self) -> &PublicKeys {
        self
    }
}

impl AsRef<SigningPublicKey> for PublicKeys {
    fn as_ref(&self) -> &SigningPublicKey {
        &self.signing_public_key
    }
}

impl AsRef<EncapsulationPublicKey> for PublicKeys {
    fn as_ref(&self) -> &EncapsulationPublicKey {
        &self.encapsulation_public_key
    }
}

impl CBORTagged for PublicKeys {
    fn cbor_tags() -> Vec<Tag> {
        tags_for_values(&[tags::TAG_PUBLIC_KEYS])
    }
}

impl From<PublicKeys> for CBOR {
    fn from(value: PublicKeys) -> Self {
        value.tagged_cbor()
    }
}

impl CBORTaggedEncodable for PublicKeys {
    fn untagged_cbor(&self) -> CBOR {
        let signing_key_cbor: CBOR = self.signing_public_key.clone().into();
        let encapsulation_key_cbor: CBOR = self.encapsulation_public_key.clone().into();
        vec![signing_key_cbor, encapsulation_key_cbor].into()
    }
}

impl TryFrom<CBOR> for PublicKeys {
    type Error = Error;

    fn try_from(cbor: CBOR) -> Result<Self, Self::Error> {
        Self::from_tagged_cbor(cbor)
    }
}

impl CBORTaggedDecodable for PublicKeys {
    fn from_untagged_cbor(untagged_cbor: CBOR) -> Result<Self> {
        match untagged_cbor.as_case() {
            CBORCase::Array(elements) => {
                if elements.len() != 2 {
                    bail!("PublicKeys must have two elements");
                }

                let signing_public_key = SigningPublicKey::try_from(elements[0].clone())?;
                let encapsulation_public_key = EncapsulationPublicKey::try_from(
                    elements[1].clone()
                )?;
                Ok(Self::new(signing_public_key, encapsulation_public_key))
            }
            _ => bail!("PublicKeys must be an array"),
        }
    }
}

impl Verifier for PublicKeys {
    fn verify(&self, signature: &Signature, message: &dyn AsRef<[u8]>) -> bool {
        self.signing_public_key.verify(signature, message)
    }
}

impl Encrypter for PublicKeys {
    fn encapsulation_public_key(&self) -> EncapsulationPublicKey {
        self.encapsulation_public_key.clone()
    }
}

impl std::fmt::Display for PublicKeys {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "PublicKeys({})", self.reference().ref_hex_short())
    }
}

#[cfg(test)]
mod tests {
    use bc_ur::{ UREncodable, URDecodable };
    use hex_literal::hex;
    use dcbor::prelude::*;

    use crate::{ PrivateKeyBase, PublicKeys, PublicKeysProvider, ReferenceProvider };

    const SEED: [u8; 16] = hex!("59f2293a5bce7d4de59e71b4207ac5d2");

    #[test]
    fn test_private_key_base() {
        crate::register_tags();
        let private_key_base = PrivateKeyBase::from_data(SEED);
        let public_keys = private_key_base.public_keys();

        let cbor = CBOR::from(public_keys.clone());

        let public_keys_2 = PublicKeys::try_from(cbor.clone()).unwrap();
        assert_eq!(public_keys, public_keys_2);

        let cbor_2 = CBOR::from(public_keys_2);
        assert_eq!(cbor, cbor_2);

        let ur = public_keys.ur_string();
        assert_eq!(
            ur,
            "ur:crypto-pubkeys/lftanshfhdcxzcgtcpytvsgafsondpjkbkoxaopsnniycawpnbnlwsgtregdfhgynyjksrgafmcstansgrhdcxlnfnwfzstovlrdfeuoghvwwyuesbcltsmetbgeurpfoyswfrzojlwdenjzckvadnrndtgsya"
        );
        assert_eq!(PublicKeys::from_ur_string(&ur).unwrap(), public_keys);

        assert_eq!(format!("{}", public_keys), "PublicKeys(c9ede672)");
        assert_eq!(format!("{}", public_keys.reference()), "Reference(c9ede672)");
    }
}