/// <summary>
/// Verify the signature of the message headers.
/// </summary>
/// <remarks>
/// Verifies the signature of the message headers.
/// </remarks>
/// <param name="options">The formatting options.</param>
/// <param name="message">The signed MIME message.</param>
/// <param name="dkimSignature">The DKIM-Signature or ARC-Message-Signature header.</param>
/// <param name="signatureAlgorithm">The algorithm used to sign the message headers.</param>
/// <param name="key">The public key used to verify the signature.</param>
/// <param name="headers">The list of headers that were signed.</param>
/// <param name="canonicalizationAlgorithm">The algorithm used to canonicalize the headers.</param>
/// <param name="signature">The expected signature of the headers encoded in base64.</param>
/// <returns><c>true</c> if the calculated signature matches <paramref name="signature"/>; otherwise, <c>false</c>.</returns>
protected bool VerifySignature(FormatOptions options, MimeMessage message, Header dkimSignature, DkimSignatureAlgorithm signatureAlgorithm, AsymmetricKeyParameter key, string[] headers, DkimCanonicalizationAlgorithm canonicalizationAlgorithm, string signature)
{
using (var stream = new DkimSignatureStream(CreateVerifyContext(signatureAlgorithm, key))) {
using (var filtered = new FilteredStream(stream)) {
filtered.Add(options.CreateNewLineFilter());
WriteHeaders(options, message, headers, canonicalizationAlgorithm, filtered);
// now include the DKIM-Signature header that we are verifying,
// but only after removing the "b=" signature value.
var header = GetSignedSignatureHeader(dkimSignature);
switch (canonicalizationAlgorithm)
{
case DkimCanonicalizationAlgorithm.Relaxed:
WriteHeaderRelaxed(options, filtered, header, true);
break;
default:
WriteHeaderSimple(options, filtered, header, true);
break;
}
filtered.Flush();
}
return(stream.VerifySignature(signature));
}
}
async Task <bool> VerifyArcSealAsync(FormatOptions options, ArcHeaderSet[] sets, int i, bool doAsync, CancellationToken cancellationToken)
{
DkimSignatureAlgorithm algorithm;
AsymmetricKeyParameter key;
string d, s, q, b;
ValidateArcSealParameters(sets[i].ArcSealParameters, out algorithm, out d, out s, out q, out b);
if (!IsEnabled(algorithm))
{
return(false);
}
if (doAsync)
{
key = await PublicKeyLocator.LocatePublicKeyAsync(q, d, s, cancellationToken).ConfigureAwait(false);
}
else
{
key = PublicKeyLocator.LocatePublicKey(q, d, s, cancellationToken);
}
if ((key is RsaKeyParameters rsa) && rsa.Modulus.BitLength < MinimumRsaKeyLength)
{
return(false);
}
options = options.Clone();
options.NewLineFormat = NewLineFormat.Dos;
using (var stream = new DkimSignatureStream(CreateVerifyContext(algorithm, key))) {
using (var filtered = new FilteredStream(stream)) {
filtered.Add(options.CreateNewLineFilter());
for (int j = 0; j < i; j++)
{
WriteHeaderRelaxed(options, filtered, sets[j].ArcAuthenticationResult, false);
WriteHeaderRelaxed(options, filtered, sets[j].ArcMessageSignature, false);
WriteHeaderRelaxed(options, filtered, sets[j].ArcSeal, false);
}
WriteHeaderRelaxed(options, filtered, sets[i].ArcAuthenticationResult, false);
WriteHeaderRelaxed(options, filtered, sets[i].ArcMessageSignature, false);
// now include the ARC-Seal header that we are verifying,
// but only after removing the "b=" signature value.
var seal = GetSignedSignatureHeader(sets[i].ArcSeal);
WriteHeaderRelaxed(options, filtered, seal, true);
filtered.Flush();
}
return(stream.VerifySignature(b));
}
}
Header GenerateArcMessageSignature(FormatOptions options, MimeMessage message, int instance, TimeSpan t, IList <string> headers)
{
if (message.MimeVersion == null && message.Body != null && message.Body.Headers.Count > 0)
{
message.MimeVersion = new Version(1, 0);
}
var value = CreateArcHeaderBuilder(instance);
byte[] signature, hash;
Header ams;
value.AppendFormat("; d={0}; s={1}", Domain, Selector);
value.AppendFormat("; c={0}/{1}",
HeaderCanonicalizationAlgorithm.ToString().ToLowerInvariant(),
BodyCanonicalizationAlgorithm.ToString().ToLowerInvariant());
value.AppendFormat("; t={0}", (long)t.TotalSeconds);
using (var stream = new DkimSignatureStream(CreateSigningContext())) {
using (var filtered = new FilteredStream(stream)) {
filtered.Add(options.CreateNewLineFilter());
// write the specified message headers
DkimVerifierBase.WriteHeaders(options, message, headers, HeaderCanonicalizationAlgorithm, filtered);
value.AppendFormat("; h={0}", string.Join(":", headers.ToArray()));
hash = message.HashBody(options, SignatureAlgorithm, BodyCanonicalizationAlgorithm, -1);
value.AppendFormat("; bh={0}", Convert.ToBase64String(hash));
value.Append("; b=");
ams = new Header(HeaderId.ArcMessageSignature, value.ToString());
switch (HeaderCanonicalizationAlgorithm)
{
case DkimCanonicalizationAlgorithm.Relaxed:
DkimVerifierBase.WriteHeaderRelaxed(options, filtered, ams, true);
break;
default:
DkimVerifierBase.WriteHeaderSimple(options, filtered, ams, true);
break;
}
filtered.Flush();
}
signature = stream.GenerateSignature();
ams.Value += Convert.ToBase64String(signature);
return(ams);
}
}
Header GenerateArcSeal(FormatOptions options, int instance, TimeSpan t, ArcHeaderSet[] sets, int count, Header aar, Header ams)
{
var value = CreateArcHeaderBuilder(instance);
byte[] signature;
Header seal;
// FIXME: where should this value come from?
value.Append("; cv=pass");
value.AppendFormat("; d={0}; s={1}", Domain, Selector);
value.AppendFormat("; t={0}", (long)t.TotalSeconds);
using (var stream = new DkimSignatureStream(CreateSigningContext())) {
using (var filtered = new FilteredStream(stream)) {
filtered.Add(options.CreateNewLineFilter());
for (int i = 0; i < count; i++)
{
DkimVerifierBase.WriteHeaderRelaxed(options, filtered, sets[i].ArcAuthenticationResult, false);
DkimVerifierBase.WriteHeaderRelaxed(options, filtered, sets[i].ArcMessageSignature, false);
DkimVerifierBase.WriteHeaderRelaxed(options, filtered, sets[i].ArcSeal, false);
}
DkimVerifierBase.WriteHeaderRelaxed(options, filtered, aar, false);
DkimVerifierBase.WriteHeaderRelaxed(options, filtered, ams, false);
value.Append("; b=");
seal = new Header(HeaderId.ArcSeal, value.ToString());
DkimVerifierBase.WriteHeaderRelaxed(options, filtered, seal, true);
filtered.Flush();
}
signature = stream.GenerateSignature();
seal.Value += Convert.ToBase64String(signature);
return(seal);
}
}
async Task <bool> VerifyAsync(FormatOptions options, MimeMessage message, Header dkimSignature, bool doAsync, CancellationToken cancellationToken)
{
if (options == null)
{
throw new ArgumentNullException(nameof(options));
}
if (message == null)
{
throw new ArgumentNullException(nameof(message));
}
if (dkimSignature == null)
{
throw new ArgumentNullException(nameof(dkimSignature));
}
if (dkimSignature.Id != HeaderId.DkimSignature)
{
throw new ArgumentException("The signature parameter MUST be a DKIM-Signature header.", nameof(dkimSignature));
}
var parameters = ParseParameterTags(dkimSignature.Id, dkimSignature.Value);
DkimCanonicalizationAlgorithm headerAlgorithm, bodyAlgorithm;
DkimSignatureAlgorithm signatureAlgorithm;
AsymmetricKeyParameter key;
string d, s, q, bh, b;
string[] headers;
int maxLength;
ValidateDkimSignatureParameters(parameters, out signatureAlgorithm, out headerAlgorithm, out bodyAlgorithm,
out d, out s, out q, out headers, out bh, out b, out maxLength);
if (!IsEnabled(signatureAlgorithm))
{
return(false);
}
if (doAsync)
{
key = await PublicKeyLocator.LocatePublicKeyAsync(q, d, s, cancellationToken).ConfigureAwait(false);
}
else
{
key = PublicKeyLocator.LocatePublicKey(q, d, s, cancellationToken);
}
if ((key is RsaKeyParameters rsa) && rsa.Modulus.BitLength < MinimumRsaKeyLength)
{
return(false);
}
options = options.Clone();
options.NewLineFormat = NewLineFormat.Dos;
// first check the body hash (if that's invalid, then the entire signature is invalid)
var hash = Convert.ToBase64String(message.HashBody(options, signatureAlgorithm, bodyAlgorithm, maxLength));
if (hash != bh)
{
return(false);
}
using (var stream = new DkimSignatureStream(CreateVerifyContext(signatureAlgorithm, key))) {
using (var filtered = new FilteredStream(stream)) {
filtered.Add(options.CreateNewLineFilter());
WriteHeaders(options, message, headers, headerAlgorithm, filtered);
// now include the DKIM-Signature header that we are verifying,
// but only after removing the "b=" signature value.
var header = GetSignedSignatureHeader(dkimSignature);
switch (headerAlgorithm)
{
case DkimCanonicalizationAlgorithm.Relaxed:
WriteHeaderRelaxed(options, filtered, header, true);
break;
default:
WriteHeaderSimple(options, filtered, header, true);
break;
}
filtered.Flush();
}
return(stream.VerifySignature(b));
}
}
void DkimSign(FormatOptions options, MimeMessage message, IList <string> headers)
{
var value = new StringBuilder("v=1");
var t = GetTimestamp();
byte[] signature, hash;
Header dkim;
options = options.Clone();
options.NewLineFormat = NewLineFormat.Dos;
options.EnsureNewLine = true;
switch (SignatureAlgorithm)
{
case DkimSignatureAlgorithm.Ed25519Sha256:
value.Append("; a=ed25519-sha256");
break;
case DkimSignatureAlgorithm.RsaSha256:
value.Append("; a=rsa-sha256");
break;
default:
value.Append("; a=rsa-sha1");
break;
}
value.AppendFormat("; d={0}; s={1}", Domain, Selector);
value.AppendFormat("; c={0}/{1}",
HeaderCanonicalizationAlgorithm.ToString().ToLowerInvariant(),
BodyCanonicalizationAlgorithm.ToString().ToLowerInvariant());
if (!string.IsNullOrEmpty(QueryMethod))
{
value.AppendFormat("; q={0}", QueryMethod);
}
if (!string.IsNullOrEmpty(AgentOrUserIdentifier))
{
value.AppendFormat("; i={0}", AgentOrUserIdentifier);
}
value.AppendFormat("; t={0}", t);
using (var stream = new DkimSignatureStream(CreateSigningContext())) {
using (var filtered = new FilteredStream(stream)) {
filtered.Add(options.CreateNewLineFilter());
// write the specified message headers
DkimVerifierBase.WriteHeaders(options, message, headers, HeaderCanonicalizationAlgorithm, filtered);
value.AppendFormat("; h={0}", string.Join(":", headers.ToArray()));
hash = message.HashBody(options, SignatureAlgorithm, BodyCanonicalizationAlgorithm, -1);
value.AppendFormat("; bh={0}", Convert.ToBase64String(hash));
value.Append("; b=");
dkim = new Header(HeaderId.DkimSignature, value.ToString());
message.Headers.Insert(0, dkim);
switch (HeaderCanonicalizationAlgorithm)
{
case DkimCanonicalizationAlgorithm.Relaxed:
DkimVerifierBase.WriteHeaderRelaxed(options, filtered, dkim, true);
break;
default:
DkimVerifierBase.WriteHeaderSimple(options, filtered, dkim, true);
break;
}
filtered.Flush();
}
signature = stream.GenerateSignature();
dkim.Value += Convert.ToBase64String(signature);
}
}
