private string FormatSubjectAlternativeName(byte[] rawData)
{
// Because SubjectAlternativeName is a commonly parsed structure, we'll
// specifically format this one. And we'll match the OpenSSL format, which
// includes not localizing any of the values (or respecting the multiLine boolean)
//
// The intent here is to be functionally equivalent to OpenSSL GENERAL_NAME_print.
// The end size of this string is hard to predict.
// * dNSName values have a tag that takes four characters to represent ("DNS:")
// and then their payload is ASCII encoded (so one byte -> one char), so they
// work out to be about equal (in chars) to their DER encoded length (in bytes).
// * iPAddress values have a tag that takes 11 characters ("IP Address:") and then
// grow from 4 bytes to up to 15 characters for IPv4, or 16 bytes to 47 characters
// for IPv6
//
// So use a List<string> and just Concat them all when we're done, and we reduce the
// number of times we copy the header values (vs pointers to the header values).
List <string> segments = new List <string>();
try
{
// SubjectAltName ::= GeneralNames
//
// GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName
//
// GeneralName ::= CHOICE {
// otherName [0] OtherName,
// rfc822Name [1] IA5String,
// dNSName [2] IA5String,
// x400Address [3] ORAddress,
// directoryName [4] Name,
// ediPartyName [5] EDIPartyName,
// uniformResourceIdentifier [6] IA5String,
// iPAddress [7] OCTET STRING,
// registeredID [8] OBJECT IDENTIFIER }
//
// OtherName::= SEQUENCE {
// type - id OBJECT IDENTIFIER,
// value[0] EXPLICIT ANY DEFINED BY type - id }
DerSequenceReader altNameReader = new DerSequenceReader(rawData);
while (altNameReader.HasData)
{
if (segments.Count != 0)
{
segments.Add(CommaSpace);
}
byte tag = altNameReader.PeekTag();
if ((tag & DerSequenceReader.ContextSpecificTagFlag) == 0)
{
// All GeneralName values need the ContextSpecific flag.
return(null);
}
GeneralNameType nameType = (GeneralNameType)(tag & DerSequenceReader.TagNumberMask);
bool needsConstructedFlag = false;
switch (nameType)
{
case GeneralNameType.OtherName:
case GeneralNameType.X400Address:
case GeneralNameType.DirectoryName:
case GeneralNameType.EdiPartyName:
needsConstructedFlag = true;
break;
}
if (needsConstructedFlag &&
(tag & DerSequenceReader.ConstructedFlag) == 0)
{
// All of the SEQUENCE types require the constructed bit,
// or OpenSSL will have refused to print it.
return(null);
}
switch (nameType)
{
case GeneralNameType.OtherName:
segments.Add("othername:<unsupported>");
altNameReader.SkipValue();
break;
case GeneralNameType.Rfc822Name:
segments.Add("email:");
segments.Add(altNameReader.ReadIA5String());
break;
case GeneralNameType.DnsName:
segments.Add("DNS:");
segments.Add(altNameReader.ReadIA5String());
break;
case GeneralNameType.X400Address:
segments.Add("X400Name:<unsupported>");
altNameReader.SkipValue();
break;
case GeneralNameType.DirectoryName:
// OpenSSL supports printing one of these, but the logic lives in X509Certificates,
// and it isn't very common. So we'll skip this one until someone asks for it.
segments.Add("DirName:<unsupported>");
altNameReader.SkipValue();
break;
case GeneralNameType.EdiPartyName:
segments.Add("EdiPartyName:<unsupported>");
altNameReader.SkipValue();
break;
case GeneralNameType.UniformResourceIdentifier:
segments.Add("URI:");
segments.Add(altNameReader.ReadIA5String());
break;
case GeneralNameType.IPAddress:
segments.Add("IP Address");
byte[] ipAddressBytes = altNameReader.ReadOctetString();
if (ipAddressBytes.Length == 4)
{
// Add the colon and dotted-decimal representation of IPv4.
segments.Add(
$":{ipAddressBytes[0]}.{ipAddressBytes[1]}.{ipAddressBytes[2]}.{ipAddressBytes[3]}");
}
else if (ipAddressBytes.Length == 16)
{
// Print the IP Address value as colon separated UInt16 hex values without leading zeroes.
// 20 01 0D B8 AC 10 FE 01 00 00 00 00 00 00 00 00
//
// IP Address:2001:DB8:AC10:FE01:0:0:0:0
for (int i = 0; i < ipAddressBytes.Length; i += 2)
{
segments.Add($":{ipAddressBytes[i] << 8 | ipAddressBytes[i + 1]:X}");
}
}
else
{
segments.Add(":<invalid>");
}
break;
case GeneralNameType.RegisteredId:
segments.Add("Registered ID:");
segments.Add(altNameReader.ReadOidAsString());
break;
default:
// A new extension to GeneralName could legitimately hit this,
// but it's correct to say that until we know what that is that
// the pretty-print has failed, and we should fall back to hex.
//
// But it could also simply be poorly encoded user data.
return(null);
}
}
return(string.Concat(segments));
}
catch (CryptographicException)
{
return(null);
}
}