Functions/Get-Asn1LengthOctets.ps1
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.SYNOPSIS Returns ASN.1 Length Octets for a given Object Length See http://luca.ntop.org/Teaching/Appunti/asn1.html #> Function Get-Asn1LengthOctets { param ( [Parameter(Mandatory=$True)] [ValidateNotNull()] # ValidateRange, what's the Maximum? Is int even sufficient? [int] $strLen ) <# Sample Output: 127 -> 7F 128 -> 8180 (First Number to use Long form) 255 -> 81FF 256 -> 820100 (First Number to spawn 2nd Octet) 65535 -> 82FFFF 65536 -> 83010000 (First Number to spawn 3rd Octet) #> $strLen = $strLen / 2 $NumBits = ([Convert]::ToString($strLen,2)).Length $NumOctets = [int]([Math]::Ceiling($NumBits / 8)) # 0...127 = one Octet If ($NumBits -le 7) { # - Short form (for lengths between 0 and 127). One octet. # Bit 8 has value "0" and bits 7-1 give the length. $HexObject = [String]::Format("{0:X2}", $strLen) } Else { # - Long form. Two to 127 octets. # Second and following octets give the length, base 256, most significant digit first. $HexObject = [String]::Format("{0:X$($NumOctets * 2)}", $strLen) # Bit 8 of first octet has value "1" and bits 7-1 give the number of additional length octets. $HexObject = [String]::Format("{0:X2}", 128 + $NumOctets) + $HexObject } $HexObject } |