(PowerShell) Extract TSTInfo from RFC3161 Timestamp Reply

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Sends an RFC 3161 timestamp request to a TSA (Timestamp Authority) server and converts the timestamp reply to XML, and then extracts the TSTInfo from the XML and converts it to XML.

For more information, see https://www.ietf.org/rfc/rfc3161.txt

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Add-Type -Path "C:\chilkat\ChilkatDotNet47-9.5.0-x64\ChilkatDotNet47.dll"

# Note: Requires Chilkat v9.5.0.75 or greater.

# This requires the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

# First sha-256 hash the data that is to be timestamped.
# In this example, the data is the string "Hello World"

$crypt = New-Object Chilkat.Crypt2
$crypt.HashAlgorithm = "sha256"
$crypt.EncodingMode = "base64"
$base64Hash = $crypt.HashFileENC("qa_data/hamlet.xml")

$http = New-Object Chilkat.Http

$requestToken = New-Object Chilkat.BinData
$optionalPolicyOid = ""
$addNonce = $false
$requestTsaCert = $true

# Create a time-stamp request token
$success = $http.CreateTimestampRequest("sha256",$base64Hash,$optionalPolicyOid,$addNonce,$requestTsaCert,$requestToken)
if ($success -eq $false) {
    $($http.LastErrorText)
    exit
}

# Send the time-stamp request token to the TSA.
# This is the equivalent of the following CURL command:
# curl -H "Content-Type: application/timestamp-query" --data-binary '@file.tsq' http://timestamp.digicert.com > file.tsr
$tsaUrl = "http://timestamp.digicert.com"
$resp = $http.PBinaryBd("POST",$tsaUrl,$requestToken,"application/timestamp-query",$false,$false)
if ($http.LastMethodSuccess -eq $false) {
    $($http.LastErrorText)
    exit
}

# Get the timestamp reply from the HTTP response object.
$timestampReply = New-Object Chilkat.BinData
$resp.GetBodyBd($timestampReply)

# Convert the binary timestamp reply to XML
$asn = New-Object Chilkat.Asn
$success = $asn.LoadBd($timestampReply)
if ($success -eq $false) {
    $($asn.LastErrorText)
    exit
}

$xml = New-Object Chilkat.Xml
$success = $xml.LoadXml($asn.AsnToXml())

# Extract the TSTInfo from the XML.
# The TSTInfo is this base64 encoded ASN.1 

# TSTInfo ::= SEQUENCE  {
#    version                      INTEGER  { v1(1) },
#    policy                       TSAPolicyId,
#    messageImprint               MessageImprint,
#      -- MUST have the same value as the similar field in
#      -- TimeStampReq
#    serialNumber                 INTEGER,
#     -- Time-Stamping users MUST be ready to accommodate integers
#     -- up to 160 bits.
#    genTime                      GeneralizedTime,
#    accuracy                     Accuracy                 OPTIONAL,
#    ordering                     BOOLEAN             DEFAULT FALSE,
#    nonce                        INTEGER                  OPTIONAL,
#      -- MUST be present if the similar field was present
#      -- in TimeStampReq.  In that case it MUST have the same value.
#    tsa                          [0] GeneralName          OPTIONAL,
#    extensions                   [1] IMPLICIT Extensions   OPTIONAL  }

$tstInfoBase64 = $xml.GetChildContent("sequence[1]|contextSpecific|sequence|sequence|contextSpecific|octets")

$bdTstInfo = New-Object Chilkat.BinData
$bdTstInfo.AppendEncoded($tstInfoBase64,"base64")

$asnTstInfo = New-Object Chilkat.Asn
$success = $asnTstInfo.LoadBd($bdTstInfo)
if ($success -eq $false) {
    $($asnTstInfo.LastErrorText)
    exit
}

$xmlTstInfo = New-Object Chilkat.Xml
$success = $xmlTstInfo.LoadXml($asnTstInfo.AsnToXml())
$($xmlTstInfo.GetXml())

# Here's the TSTInfo XML:

# <?xml version="1.0" encoding="utf-8"?>
# <sequence>
#     <int>01</int>
#     <oid>2.16.840.1.114412.7.1</oid>
#     <sequence>
#         <sequence>
#             <oid>2.16.840.1.101.3.4.2.1</oid>
#             <null/>
#         </sequence>
#         <octets>4sRRyWOzC7EOic4fQ9+Op1pa10DbgoBGjBvkq09LZmE=</octets>
#     </sequence>
#     <int>00AD2C86E49872597B60F87D5C54BCFFAE</int>
#     <universal tag="24" constructed="0">MjAyMzAzMTYxMTQ5NTJa</universal>
# </sequence>

#    The genTime (GeneralizedTime) is contained in the final "universal" XML element and is 
#    in base64. It is the time at which the time-stamp token has been created by
#    the TSA. After decoding from base64, it is:
# 
#    The syntax is: YYYYMMDDhhmmss[.s...]Z
#    Example: 19990609001326.34352Z

$sbGenTime = New-Object Chilkat.StringBuilder
$sbGenTime.DecodeAndAppend($xmlTstInfo.GetChildContent("universal"),"base64","utf-8")
$($sbGenTime.GetAsString())

# Result:
# 20230316115718Z