structured-pkix 0.1.4

//! Compose signature/issuer scope with requested target, extension and time facts.

use super::{
    Digest, ExtensionProcessing, Lookup, NonceBinding, RequestNonce, ScopedResponse,
    SingleResponse, UpdateWindow,
};
use crate::error::{CallbackResult, Result};
use crate::temporal::{LeapTable, Reading};
use crate::{Certificate, Error};
use structured_asn1::memory::{Memory, MemoryError};
use structured_asn1::{Oid, Span};

/// Actual caller request facts, never inferred from the received response.
pub struct Request<'p, 'a> {
    /// Certificate identified by the actual request and authenticated issuer path.
    pub target: &'p Certificate<'a>,
    /// Actual sent nonce, not a newly generated replacement.
    pub nonce: Option<RequestNonce<'p>>,
    /// Optional expected exact signer certificate chosen by the caller. Absent
    /// binding is reported explicitly rather than counted as a match.
    pub intended_signer: Option<&'p Certificate<'a>>,
}

/// Current temporal/resource facts; maximum age and clock-skew policy stay outside.
pub struct Evaluation<'p> {
    /// Actual caller-supplied current label, retaining subnanosecond precision.
    pub now: Reading,
    /// Caller-authenticated UTC correction evidence and explicit coverage.
    pub utc: &'p LeapTable<'p>,
    /// Current operation's shared work and storage domain.
    pub execution: &'p Memory,
}

/// Whether this evidence is bound to the caller's exact intended signer input.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RecipientBinding {
    /// Caller did not supply an exact signer; no such claim is made.
    NotSpecified,
    /// Authenticated actual signer matches the supplied exact certificate.
    Matches,
}

/// Composed original evidence, still not final application acceptance. Read its
/// authority source for pending delegate revocation, and apply nonce, maximum
/// age, recipient and time-uncertainty policy before interpreting status.
#[derive(Debug, Clone, Copy)]
pub struct Evidence<'r, 'a> {
    source: ScopedResponse<'r, 'a>,
    assertion: &'r SingleResponse<'a>,
    window: UpdateWindow,
    nonce: NonceBinding,
    recipient: RecipientBinding,
    revocation_time: Option<crate::time::Relation>,
}

impl<'r, 'a> Evidence<'r, 'a> {
    /// Signature and explicit issuer-scope provenance.
    #[must_use]
    pub fn source(self) -> ScopedResponse<'r, 'a> {
        self.source
    }
    /// Selected original assertion, with every uninterpreted noncritical value.
    #[must_use]
    pub fn assertion(self) -> &'r SingleResponse<'a> {
        self.assertion
    }
    /// Update-window relation, not a maximum-age decision.
    #[must_use]
    pub fn window(self) -> UpdateWindow {
        self.window
    }
    /// Actual request/response nonce relation.
    #[must_use]
    pub fn nonce(self) -> NonceBinding {
        self.nonce
    }
    /// Exact intended signer binding, when requested.
    #[must_use]
    pub fn recipient(self) -> RecipientBinding {
        self.recipient
    }

    /// UTC-qualified recorded revocation time when this assertion is revoked.
    #[must_use]
    pub fn revocation_time(self) -> Option<crate::time::Relation> {
        self.revocation_time
    }
}

/// Target processing outcome, without turning missing/unsupported into Good.
#[derive(Debug, Clone, Copy)]
pub enum TargetEvidence<'r, 'a> {
    /// Identity and supported extension semantics completed; policy facts remain.
    Evidence(Evidence<'r, 'a>),
    /// Actual signer differs from the caller's intended exact signer.
    UnexpectedSigner,
    /// Identity lookup did not yield one usable assertion.
    Lookup(Lookup<'r, 'a>),
    /// Response-wide or selected-assertion critical demand cannot be processed.
    UnsupportedCritical {
        /// Original unsupported demand identifier.
        kind: Oid<'a>,
        /// Original location.
        span: Span,
    },
}

fn exact_signer(
    left: &Certificate<'_>,
    right: &Certificate<'_>,
    execution: &Memory,
    at: u64,
) -> Result<bool> {
    let left = left.as_bytes();
    let right = right.as_bytes();
    let work = u64::try_from(left.len().max(right.len()))
        .ok()
        .and_then(|n| n.checked_mul(2))
        .and_then(|n| n.checked_add(1))
        .ok_or_else(|| Error::resource(MemoryError::WorkExceeded, "ocspResponse.recipient", at))?;
    execution
        .charge_work(work)
        .map_err(|reason| Error::resource(reason, "ocspResponse.recipient", at))?;
    Ok(left == right)
}

impl<'r, 'a> ScopedResponse<'r, 'a> {
    /// Evaluate the actual request against this issuer-scoped signed response.
    /// RFC6960 §3.2 requires identity, signer, authorization and temporal checks;
    /// this operation composes mechanism facts without choosing caller policy.
    /// <https://www.rfc-editor.org/rfc/rfc6960#section-3.2>
    pub fn evaluate<D: Digest>(
        self,
        request: &Request<'_, '_>,
        time: &Evaluation<'_>,
        digest: &D,
    ) -> CallbackResult<TargetEvidence<'r, 'a>, D::Error> {
        let execution = time.execution;
        let response = self.signed().response();
        let recipient = match request.intended_signer {
            None => RecipientBinding::NotSpecified,
            Some(expected) => {
                if !exact_signer(
                    self.signed().signer(),
                    expected,
                    execution,
                    response.span().start,
                )? {
                    return Ok(TargetEvidence::UnexpectedSigner);
                }
                RecipientBinding::Matches
            }
        };
        let processed = response.process_extensions(execution)?;
        if let ExtensionProcessing::Unsupported { kind, span } = processed.processing {
            return Ok(TargetEvidence::UnsupportedCritical { kind, span });
        }
        let assertion = match self.find(request.target, digest, execution)? {
            Lookup::Found(assertion) => assertion,
            outcome => return Ok(TargetEvidence::Lookup(outcome)),
        };
        if let ExtensionProcessing::Unsupported { kind, span } =
            assertion.check_extensions(execution)?
        {
            return Ok(TargetEvidence::UnsupportedCritical { kind, span });
        }
        let nonce = super::nonce::bind(
            request.nonce,
            processed.nonce,
            execution,
            response.span().start,
        )?;
        let window = assertion.update_window(time.now, time.utc, execution)?;
        let revocation_time = assertion.revocation_relation(time.now, time.utc, execution)?;
        Ok(TargetEvidence::Evidence(Evidence {
            source: self,
            assertion,
            nonce,
            window,
            recipient,
            revocation_time,
        }))
    }
}

#[cfg(test)]
mod tests;