public void DKIMSign(ISigner signer, CanonicalizationType headerCanonicalization, CanonicalizationType bodyCanonicalization, HashingAlgorithm hashAlgorithm, string domain, string selector)
{
if (IsSigned)
{
throw new InvalidOperationException("Message already have DKIM header.");
}
IsSigned = true;
string hashtype = hashAlgorithm == HashingAlgorithm.RSASha1 ? "sha1" : "sha256";
StringBuilder dkim = new StringBuilder(300)
.Append("v=1;") // version
.Append("a=").Append("rsa-").Append(hashtype).Append(";") // hash algorithm
.Append("c=").Append(string.Format("{0}/{1}", headerCanonicalization, bodyCanonicalization).ToLower()).Append(";") // canonicalization types headers/body
.Append("d=").Append(domain).Append(";") // domain for diim check
.Append("s=").Append(selector).Append(";") // TXT record selector
.Append("t=").Append(Convert.ToInt64((DateTime.Now.ToUniversalTime() - DateTime.SpecifyKind(DateTime.Parse("00:00:00 January 1, 1970"), DateTimeKind.Utc)).TotalSeconds).ToString()).Append(";") // creation time
.Append("bh=").Append(GetBodyHash(bodyCanonicalization, hashtype)).Append(";"); // body hash
var headers = ComputedHeaders;
List <string> h = new List <string>();
foreach (string header in headers)
{
foreach (string value in headers.GetValues(header))
{
h.Add(header);
}
}
dkim.Append("h=").Append(string.Join(":", h)).Append(";") // headers for hashing
.Append("b="); // signature data
var canonialized = DKIMCanonicalizer.CanonicalizeHeader(headerCanonicalization, headers) + "dkim-signature:" + dkim.ToString();
var bytes = (HeadersEncoding ?? Encoding.UTF8).GetBytes(canonialized);
lock (signer)
{
signer.BlockUpdate(bytes, 0, bytes.Length);
bytes = signer.GenerateSignature();//computing signature
signer.Reset();
}
dkim.Append(Convert.ToBase64String(bytes));
Headers.Add("dkim-signature", dkim.ToString());// adding DKIM header
}
public string GetBodyHash(CanonicalizationType type, string hashType)
{
var canonicalized = DKIMCanonicalizer.CanonicalizeBody(type, ComputedBody).TrimStart('\r', '\n');
return(Convert.ToBase64String(HashAlgorithm.Create(hashType).ComputeHash(Encoding.ASCII.GetBytes(canonicalized))));
}
