/// <summary>
/// Verify the specified DKIM-Signature header.
/// </summary>
/// <remarks>
/// Verifies the specified DKIM-Signature header.
/// </remarks>
/// <param name="options">The formatting options.</param>
/// <param name="dkimSignature">The DKIM-Signature header.</param>
/// <param name="publicKeyLocator">The public key locator service.</param>
/// <param name="cancellationToken">The cancellation token.</param>
/// <exception cref="System.ArgumentNullException">
/// <para><paramref name="options"/> is <c>null</c>.</para>
/// <para>-or-</para>
/// <para><paramref name="dkimSignature"/> is <c>null</c>.</para>
/// <para>-or-</para>
/// <para><paramref name="publicKeyLocator"/> is <c>null</c>.</para>
/// </exception>
/// <exception cref="System.ArgumentException">
/// <paramref name="dkimSignature"/> is not a DKIM-Signature header.
/// </exception>
/// <exception cref="System.FormatException">
/// The DKIM-Signature header value is malformed.
/// </exception>
/// <exception cref="System.OperationCanceledException">
/// The operation was canceled via the cancellation token.
/// </exception>
bool Verify (FormatOptions options, Header dkimSignature, IDkimPublicKeyLocator publicKeyLocator, CancellationToken cancellationToken = default (CancellationToken))
{
if (options == null)
throw new ArgumentNullException ("options");
if (dkimSignature == null)
throw new ArgumentNullException ("dkimSignature");
if (dkimSignature.Id != HeaderId.DkimSignature)
throw new ArgumentException ("The dkimSignature parameter MUST be a DKIM-Signature header.", "dkimSignature");
if (publicKeyLocator == null)
throw new ArgumentNullException ("publicKeyLocator");
var parameters = ParseDkimSignature (dkimSignature.Value);
DkimCanonicalizationAlgorithm headerAlgorithm, bodyAlgorithm;
DkimSignatureAlgorithm signatureAlgorithm;
AsymmetricKeyParameter key;
string d, s, q, h, bh, b;
int maxLength;
ValidateDkimSignatureParameters (parameters, out signatureAlgorithm, out headerAlgorithm, out bodyAlgorithm,
out d, out s, out q, out h, out bh, out b, out maxLength);
key = publicKeyLocator.LocatePublicKey (q, d, s, cancellationToken);
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 (DkimHashBody (options, signatureAlgorithm, bodyAlgorithm, maxLength));
if (hash != bh)
return false;
using (var stream = new DkimSignatureStream (DkimGetDigestSigner (signatureAlgorithm, key))) {
using (var filtered = new FilteredStream (stream)) {
filtered.Add (options.CreateNewLineFilter ());
DkimWriteHeaders (options, h.Split (':'), headerAlgorithm, filtered);
// now include the DKIM-Signature header that we are verifying,
// but only after removing the "b=" signature value.
var header = GetSignedDkimSignatureHeader (dkimSignature);
switch (headerAlgorithm) {
case DkimCanonicalizationAlgorithm.Relaxed:
DkimWriteHeaderRelaxed (options, filtered, header);
break;
default:
DkimWriteHeaderSimple (options, filtered, header);
break;
}
filtered.Flush ();
}
return stream.VerifySignature (b);
}
}
