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package poseidon
import ( "fmt" "math/big"
"github.com/iden3/go-iden3-crypto/ff" "github.com/iden3/go-iden3-crypto/utils" )
const NROUNDSF = 8 //nolint:golint
var NROUNDSP = []int{56, 57, 56, 60, 60, 63, 64, 63, 60, 66, 60, 65, 70, 60, 64, 68} //nolint:golint
func zero() *ff.Element { return ff.NewElement() }
// exp5 performs x^5 mod p
// https://eprint.iacr.org/2019/458.pdf page 8
func exp5(a *ff.Element) { a.Exp(*a, 5) //nolint:gomnd
}
// exp5state perform exp5 for whole state
func exp5state(state []*ff.Element) { for i := 0; i < len(state); i++ { exp5(state[i]) } }
// ark computes Add-Round Key, from the paper https://eprint.iacr.org/2019/458.pdf
func ark(state []*ff.Element, c []*ff.Element, it int) { for i := 0; i < len(state); i++ { state[i].Add(state[i], c[it+i]) } }
// mix returns [[matrix]] * [vector]
func mix(state []*ff.Element, t int, m [][]*ff.Element) []*ff.Element { mul := zero() newState := make([]*ff.Element, t) for i := 0; i < t; i++ { newState[i] = zero() } for i := 0; i < len(state); i++ { newState[i].SetUint64(0) for j := 0; j < len(state); j++ { mul.Mul(m[j][i], state[j]) newState[i].Add(newState[i], mul) } } return newState }
// Hash computes the Poseidon hash for the given inputs
func Hash(inpBI []*big.Int) (*big.Int, error) { t := len(inpBI) + 1 if len(inpBI) == 0 || len(inpBI) > len(NROUNDSP) { return nil, fmt.Errorf("invalid inputs length %d, max %d", len(inpBI), len(NROUNDSP)) //nolint:gomnd,lll
} inp := utils.BigIntArrayToElementArray(inpBI[:])
nRoundsF := NROUNDSF nRoundsP := NROUNDSP[t-2] C := c.c[t-2] S := c.s[t-2] M := c.m[t-2] P := c.p[t-2]
state := make([]*ff.Element, t) state[0] = zero() copy(state[1:], inp[:])
ark(state, C, 0)
for i := 0; i < nRoundsF/2-1; i++ { exp5state(state) ark(state, C, (i+1)*t) state = mix(state, t, M) } exp5state(state) ark(state, C, (nRoundsF/2)*t) state = mix(state, t, P)
for i := 0; i < nRoundsP; i++ { exp5(state[0]) state[0].Add(state[0], C[(nRoundsF/2+1)*t+i])
mul := zero() newState0 := zero() for j := 0; j < len(state); j++ { mul.Mul(S[(t*2-1)*i+j], state[j]) newState0.Add(newState0, mul) }
for k := 1; k < t; k++ { mul = zero() state[k] = state[k].Add(state[k], mul.Mul(state[0], S[(t*2-1)*i+t+k-1])) } state[0] = newState0 }
for i := 0; i < nRoundsF/2-1; i++ { exp5state(state) ark(state, C, (nRoundsF/2+1)*t+nRoundsP+i*t) state = mix(state, t, M) } exp5state(state) state = mix(state, t, M)
rE := state[0] r := big.NewInt(0) rE.ToBigIntRegular(r) return r, nil }
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