Private/Digest/Get-SecretSharingDigestConstant.ps1

function Get-SecretSharingDigestConstant {
    <#
    .SYNOPSIS
        Returns the SLIP-0039 constants used for shared-secret digest verification.
    .DESCRIPTION
        Per SLIP-0039: polynomial index 254 encodes the shared secret's digest share,
        index 255 encodes the shared secret itself, and the digest is truncated to its
        first 4 bytes. Index 255 (not 0) is used for the secret specifically so a
        combiner that forgets to validate x-coordinates can't be tricked by a share
        maliciously modified to x=0.
    #>

    [CmdletBinding()]
    [OutputType([PSCustomObject])]
    param()

    return [PSCustomObject]@{
        DigestIndex  = [byte]254
        SecretIndex  = [byte]255
        DigestLength = 4
    }
}