1use crate::{
  2    hash::rpo::Rpo256,
  3    utils::{ByteReader, ByteWriter, Deserializable, DeserializationError, Serializable},
  4    Felt, Word, ZERO,
  5};
  6
  7mod hash_to_point;
  8mod keys;
  9mod math;
 10mod signature;
 11
 12pub use self::keys::{PubKeyPoly, PublicKey, SecretKey};
 13pub use self::math::Polynomial;
 14pub use self::signature::{Signature, SignatureHeader, SignaturePoly};
 15
 16// CONSTANTS
 17// ================================================================================================
 18
 19// The Falcon modulus p.
 20const MODULUS: i16 = 12289;
 21
 22// Number of bits needed to encode an element in the Falcon field.
 23const FALCON_ENCODING_BITS: u32 = 14;
 24
 25// The Falcon parameters for Falcon-512. This is the degree of the polynomial `phi := x^N + 1`
 26// defining the ring Z_p[x]/(phi).
 27const N: usize = 512;
 28const LOG_N: u8 = 9;
 29
 30/// Length of nonce used for key-pair generation.
 31const SIG_NONCE_LEN: usize = 40;
 32
 33/// Number of filed elements used to encode a nonce.
 34const NONCE_ELEMENTS: usize = 8;
 35
 36/// Public key length as a u8 vector.
 37pub const PK_LEN: usize = 897;
 38
 39/// Secret key length as a u8 vector.
 40pub const SK_LEN: usize = 1281;
 41
 42/// Signature length as a u8 vector.
 43const SIG_POLY_BYTE_LEN: usize = 625;
 44
 45/// Bound on the squared-norm of the signature.
 46const SIG_L2_BOUND: u64 = 34034726;
 47
 48/// Standard deviation of the Gaussian over the lattice.
 49const SIGMA: f64 = 165.7366171829776;
 50
 51// TYPE ALIASES
 52// ================================================================================================
 53
 54type ShortLatticeBasis = [Polynomial<i16>; 4];
 55
 56// NONCE
 57// ================================================================================================
 58
 59/// Nonce of the Falcon signature.
 60#[derive(Debug, Clone, PartialEq, Eq)]
 61pub struct Nonce([u8; SIG_NONCE_LEN]);
 62
 63impl Nonce {
 64    /// Returns a new [Nonce] instantiated from the provided bytes.
 65    pub fn new(bytes: [u8; SIG_NONCE_LEN]) -> Self {
 66        Self(bytes)
 67    }
 68
 69    /// Returns the underlying bytes of this nonce.
 70    pub fn as_bytes(&self) -> &[u8; SIG_NONCE_LEN] {
 71        &self.0
 72    }
 73
 74    /// Converts byte representation of the nonce into field element representation.
 75    ///
 76    /// Nonce bytes are converted to field elements by taking consecutive 5 byte chunks
 77    /// of the nonce and interpreting them as field elements.
 78    pub fn to_elements(&self) -> [Felt; NONCE_ELEMENTS] {
 79        let mut buffer = [0_u8; 8];
 80        let mut result = [ZERO; 8];
 81        for (i, bytes) in self.0.chunks(5).enumerate() {
 82            buffer[..5].copy_from_slice(bytes);
 83            // we can safely (without overflow) create a new Felt from u64 value here since this
 84            // value contains at most 5 bytes
 85            result[i] = Felt::new(u64::from_le_bytes(buffer));
 86        }
 87
 88        result
 89    }
 90}
 91
 92impl Serializable for &Nonce {
 93    fn write_into<W: ByteWriter>(&self, target: &mut W) {
 94        target.write_bytes(&self.0)
 95    }
 96}
 97
 98impl Deserializable for Nonce {
 99    fn read_from<R: ByteReader>(source: &mut R) -> Result<Self, DeserializationError> {
100        let bytes = source.read()?;
101        Ok(Self(bytes))
102    }
103}