miden_core/program/
kernel.rs

1use alloc::{string::ToString, vec::Vec};
2
3use miden_crypto::{Word, hash::eidos::EidosDomain};
4
5use crate::{
6    chiplets::hasher,
7    serde::{ByteReader, ByteWriter, Deserializable, DeserializationError, Serializable},
8};
9
10// CONSTANTS
11// ================================================================================================
12
13/// Registered domain tag for the kernel commitment.
14pub const KERNEL_DOMAIN_TAG: crate::Felt = super::domain::KernelCommitmentDomain::TAG.as_felt();
15
16// KERNEL
17// ================================================================================================
18
19/// A list of exported kernel procedure hashes defining a VM kernel.
20///
21/// The internally-stored list always has a consistent order, regardless of the order of procedure
22/// list used to instantiate a descriptor.
23#[derive(Debug, Clone, Default, PartialEq, Eq)]
24#[cfg_attr(
25    all(feature = "arbitrary", test),
26    miden_test_serialization_macros::serialization_test
27)]
28pub struct KernelDescriptor(Vec<Word>);
29
30impl KernelDescriptor {
31    /// The maximum number of procedures which can be exported from a KernelDescriptor.
32    pub const MAX_NUM_PROCEDURES: usize = u8::MAX as usize;
33
34    /// Returns a new [KernelDescriptor] instantiated with the specified procedure hashes.
35    ///
36    /// Hashes are canonicalized into a consistent internal order.
37    ///
38    /// # Errors
39    /// Returns an error if:
40    /// - `proc_hashes` contains duplicates.
41    /// - `proc_hashes.len()` exceeds [`MAX_NUM_PROCEDURES`](Self::MAX_NUM_PROCEDURES).
42    pub fn new(proc_hashes: &[Word]) -> Result<Self, KernelError> {
43        Self::from_hashes(proc_hashes.to_vec())
44    }
45
46    /// Returns a new [KernelDescriptor] from owned procedure hashes.
47    ///
48    /// Hashes are canonicalized into a consistent internal order.
49    ///
50    /// # Errors
51    /// Returns an error if:
52    /// - `hashes` contains duplicates.
53    /// - `hashes.len()` exceeds [`MAX_NUM_PROCEDURES`](Self::MAX_NUM_PROCEDURES).
54    pub fn from_hashes(mut hashes: Vec<Word>) -> Result<Self, KernelError> {
55        if hashes.len() > Self::MAX_NUM_PROCEDURES {
56            return Err(KernelError::TooManyProcedures(Self::MAX_NUM_PROCEDURES, hashes.len()));
57        }
58
59        // Canonical ordering is a separate kernel invariant (not just a dedup side effect), so
60        // we sort first and then validate uniqueness over the canonical representation.
61        hashes.sort_by_key(Word::as_bytes); // ensure consistent order
62        let duplicated = hashes.windows(2).any(|data| data[0] == data[1]);
63
64        if duplicated {
65            Err(KernelError::DuplicatedProcedures)
66        } else {
67            Ok(Self(hashes))
68        }
69    }
70
71    /// Creates a kernel from raw hashes without enforcing constructor invariants.
72    ///
73    /// This is only intended for tests that need intentionally malformed kernels.
74    #[cfg(test)]
75    pub(crate) fn from_hashes_unchecked(hashes: Vec<Word>) -> Self {
76        Self(hashes)
77    }
78
79    /// Returns true if this kernel does not contain any procedures.
80    pub fn is_empty(&self) -> bool {
81        self.0.is_empty()
82    }
83
84    /// Returns true if a procedure with the specified hash belongs to this kernel.
85    ///
86    /// Note: the kernel is constructed from exported kernel procedures only.
87    pub fn contains_proc(&self, proc_hash: Word) -> bool {
88        // Note: we can't use `binary_search()` here because the hashes were sorted using a
89        // different key that the `binary_search` algorithm uses.
90        self.0.contains(&proc_hash)
91    }
92
93    /// Returns a list of procedure hashes contained in this kernel.
94    pub fn proc_hashes(&self) -> &[Word] {
95        &self.0
96    }
97
98    /// Returns the canonical commitment to this kernel: the domain-tagged sequential hash of the
99    /// flattened procedure digests, `hash_elements_in_domain(flatten(procs), KERNEL_DOMAIN_TAG)`.
100    ///
101    /// This is the fixed-size identifier observed by the recursive verifier in place of the raw
102    /// digest list. The encoding is normative:
103    /// - element order is this descriptor's canonical procedure order (fixed at construction);
104    /// - Eidos initializes its chaining word from the registered domain and exact logical length,
105    ///   preventing ambiguity between a partial block and its zero-padded form.
106    pub fn commitment(&self) -> Word {
107        hasher::hash_elements_in_domain(
108            Word::words_as_elements(&self.0),
109            super::domain::KERNEL_COMMITMENT,
110        )
111    }
112}
113
114// this is required by AIR as public inputs will be serialized with the proof
115impl Serializable for KernelDescriptor {
116    fn write_into<W: ByteWriter>(&self, target: &mut W) {
117        // expect is OK here because the number of procedures is enforced by the constructor
118        target.write_u8(self.0.len().try_into().expect("too many kernel procedures"));
119        target.write_many(&self.0)
120    }
121}
122
123impl Deserializable for KernelDescriptor {
124    fn read_from<R: ByteReader>(source: &mut R) -> Result<Self, DeserializationError> {
125        let len = source.read_u8()? as usize;
126        let kernel = source.read_many_iter::<Word>(len)?.collect::<Result<_, _>>()?;
127        Self::from_hashes(kernel).map_err(|err| DeserializationError::InvalidValue(err.to_string()))
128    }
129}
130
131// KERNEL ERROR
132// ================================================================================================
133
134#[derive(Debug, Clone, PartialEq, Eq, thiserror::Error)]
135pub enum KernelError {
136    #[error("kernel cannot have duplicated procedures")]
137    DuplicatedProcedures,
138    #[error("kernel can have at most {0} procedures, received {1}")]
139    TooManyProcedures(usize, usize),
140}
141
142#[cfg(test)]
143mod tests {
144    use alloc::vec::Vec;
145
146    use super::KernelDescriptor;
147    use crate::{
148        Felt, Word,
149        program::domain,
150        serde::{ByteWriter, Deserializable, Serializable, SliceReader},
151    };
152
153    #[test]
154    fn empty_kernel_commitment_matches_known_vector() {
155        let expected = Word::from(
156            [
157                7_629_329_411_056_522_819,
158                2_158_594_640_249_218_307,
159                769_500_264_184_883_565,
160                419_898_756_627_082_940,
161            ]
162            .map(Felt::new_unchecked),
163        );
164        let empty = KernelDescriptor::default();
165
166        assert_eq!(empty.commitment(), expected);
167        assert_eq!(
168            empty.commitment(),
169            crate::chiplets::hasher::hash_elements_in_domain(&[], domain::KERNEL_COMMITMENT)
170        );
171    }
172
173    #[test]
174    fn kernel_commitment_is_independent_of_procedure_order() {
175        let a: Word = [
176            Felt::new_unchecked(1),
177            Felt::new_unchecked(2),
178            Felt::new_unchecked(3),
179            Felt::new_unchecked(4),
180        ]
181        .into();
182        let b: Word = [
183            Felt::new_unchecked(5),
184            Felt::new_unchecked(6),
185            Felt::new_unchecked(7),
186            Felt::new_unchecked(8),
187        ]
188        .into();
189
190        // The kernel canonicalizes procedure order, so the commitment binds the set of
191        // procedures, not the order in which they were supplied.
192        let in_order = KernelDescriptor::new(&[a, b]).unwrap();
193        let reversed = KernelDescriptor::new(&[b, a]).unwrap();
194        assert_eq!(in_order.commitment(), reversed.commitment());
195    }
196
197    #[test]
198    fn kernel_read_from_rejects_duplicate_procedure_hashes() {
199        let a: Word = [
200            Felt::new_unchecked(1),
201            Felt::new_unchecked(2),
202            Felt::new_unchecked(3),
203            Felt::new_unchecked(4),
204        ]
205        .into();
206        let b: Word = [
207            Felt::new_unchecked(5),
208            Felt::new_unchecked(6),
209            Felt::new_unchecked(7),
210            Felt::new_unchecked(8),
211        ]
212        .into();
213
214        assert!(
215            KernelDescriptor::new(&[a, a]).is_err(),
216            "test precondition: KernelDescriptor::new must reject duplicates"
217        );
218
219        // Manually serialize a KernelDescriptor that contains duplicates. This cannot be
220        // constructed via `KernelDescriptor::new`, but it can be produced via the binary
221        // format.
222        let mut bytes = Vec::new();
223        bytes.write_u8(3);
224        b.write_into(&mut bytes);
225        a.write_into(&mut bytes);
226        a.write_into(&mut bytes);
227
228        let mut reader = SliceReader::new(&bytes);
229        let result = KernelDescriptor::read_from(&mut reader);
230
231        assert!(
232            result.is_err(),
233            "expected KernelDescriptor::read_from to reject duplicate procedure hashes"
234        );
235    }
236}
miden_core/program/kernel.rs

miden_core/program/
kernel.rs
