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//! Derivation context (i.e. concatenated challenges)

use challenge::{Challenge, CHALLENGE_SIZE};

/// Derivation context (i.e. concatenated challenges)
pub struct Context([u8; CHALLENGE_SIZE * 2]);

impl Context {
    /// Create a derivation context from host and card challenges
    pub fn from_challenges(host_challenge: &Challenge, card_challenge: &Challenge) -> Self {
        let mut context = [0u8; CHALLENGE_SIZE * 2];
        context[..CHALLENGE_SIZE].copy_from_slice(host_challenge.as_slice());
        context[CHALLENGE_SIZE..].copy_from_slice(card_challenge.as_slice());
        Context(context)
    }

    /// Borrow the context value as a slice
    pub fn as_slice(&self) -> &[u8] {
        &self.0
    }
}