Private/TwoFactor.ps1
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function Get-Monocle2FAInterval { [CmdletBinding()] param( [Parameter(Mandatory=$true)] [DateTime] $DateTime ) # convert to utc $DateTime = $DateTime.ToUniversalTime() # get time interval for the date $secondsPerInterval = 30 $epochTime = Get-Date "01/01/1970 00:00:00" $secondsSinceEpochTime = (New-TimeSpan -Start $epochTime -End $DateTime).TotalSeconds return [int64][math]::Floor($secondsSinceEpochTime / $secondsPerInterval) } function Get-Monocle2FAPin { [CmdletBinding()] param( [Parameter(Mandatory=$true)] [string] $Secret, [Parameter(Mandatory=$true)] [long] $Interval ) # convert the parameters to bytes $secretAsBytes = Convert-Monocle2FASecretToBytes -Secret $Secret $timeBytes = Convert-Monocle2FAIntervalToBytes -Interval $Interval # do the HMAC calculation with the default SHA1 $hmacGen = [Security.Cryptography.HMACSHA1]::new($secretAsBytes) $hash = $hmacGen.ComputeHash($timeBytes) # take half the last byte $offset = ($hash[$hash.Length - 1] -band 0xF) # use it as an index into the hash bytes and take 4 bytes from there, big-endian needed $fourBytes = $hash[$offset..($offset + 3)] if ([BitConverter]::IsLittleEndian) { [array]::Reverse($fourBytes) } # remove the most significant bit $num = ([BitConverter]::ToInt32($fourBytes, 0) -band 0x7FFFFFFF) return ($num % 1000000).ToString().PadLeft(6, '0') } function Convert-Monocle2FASecretToBytes { [CmdletBinding()] param( [Parameter(Mandatory=$true)] [string] $Secret ) $Base32Charset = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567' # convert the secret from BASE32 to a byte array via a BigInteger so we can use its bit-shifting support $bigInteger = [Numerics.BigInteger]::Zero foreach ($char in ($secret.ToUpper() -replace '[^A-Z2-7]').GetEnumerator()) { $bigInteger = (($bigInteger -shl 5) -bor ($Base32Charset.IndexOf($char))) } [byte[]]$secretAsBytes = $bigInteger.ToByteArray() # BigInteger sometimes adds a 0 byte to the end, if it happens, we need to remove it if ($secretAsBytes[-1] -eq 0) { $secretAsBytes = $secretAsBytes[0..($secretAsBytes.Count - 2)] } # BigInteger stores bytes in Little-Endian order, but we need them in Big-Endian order. [array]::Reverse($secretAsBytes) return $secretAsBytes } function Convert-Monocle2FAIntervalToBytes { [CmdletBinding()] param( [Parameter(Mandatory=$true)] [long] $Interval ) $timeBytes = [BitConverter]::GetBytes($Interval) if ([BitConverter]::IsLittleEndian) { [array]::Reverse($timeBytes) } return $timeBytes } |