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var crypto = require("crypto"),
mimelib = require("mimelib-noiconv"),
toPunycode = require("./punycode");
/**
* @namespace DKIM Signer module
* @name dkimsign
*/
module.exports.DKIMSign = DKIMSign;
module.exports.generateDKIMHeader = generateDKIMHeader;
module.exports.sha256 = sha256;
/**
* <p>Sign an email with provided DKIM key, uses RSA-SHA256.</p>
*
* @memberOf dkimsign
* @param {String} email Full e-mail source complete with headers and body to sign
* @param {Object} options DKIM options
* @param {String} [options.headerFieldNames="from:to:cc:subject"] Header fields to sign
* @param {String} options.privateKey DKMI private key
* @param {String} options.domainName Domain name to use for signing (ie: "domain.com")
* @param {String} options.keySelector Selector for the DKMI public key (ie. "dkim" if you have set up a TXT record for "dkim._domainkey.domain.com")
*
* @return {String} Signed DKIM-Signature header field for prepending
*/
function DKIMSign(email, options){
options = options || {};
email = (email || "").toString("utf-8");
var match = email.match(/^\r?\n|(?:\r?\n){2}/),
headers = match && email.substr(0, match.index) || "",
body = match && email.substr(match.index + match[0].length) || email;
// all listed fields from RFC4871 #5.5
var defaultFieldNames = "From:Sender:Reply-To:Subject:Date:Message-ID:To:" +
"Cc:MIME-Version:Content-Type:Content-Transfer-Encoding:Content-ID:" +
"Content-Description:Resent-Date:Resent-From:Resent-Sender:" +
"Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References:" +
"List-Id:List-Help:List-Unsubscribe:List-Subscribe:List-Post:" +
"List-Owner:List-Archive";
var dkim = generateDKIMHeader(options.domainName, options.keySelector, options.headerFieldNames || defaultFieldNames, headers, body),
canonicalizedHeaderData = DKIMCanonicalizer.relaxedHeaders(headers, options.headerFieldNames || defaultFieldNames),
canonicalizedDKIMHeader = DKIMCanonicalizer.relaxedHeaderLine(dkim),
signer, signature;
canonicalizedHeaderData.headers += canonicalizedDKIMHeader.key+":"+canonicalizedDKIMHeader.value;
signer = crypto.createSign("RSA-SHA256");
signer.update(canonicalizedHeaderData.headers);
signature = signer.sign(options.privateKey, 'base64');
return dkim + signature.replace(/(.{76}(?!\r?\n|\r))/g,"$&\r\n ");
}
/**
* <p>Generates a DKIM-Signature header field without the signature part ("b=" is empty)</p>
*
* @memberOf dkimsign
* @private
* @param {String} domainName Domain name to use for signing
* @param {String} keySelector Selector for the DKMI public key
* @param {String} headerFieldNames Header fields to sign
* @param {String} headers E-mail headers
* @param {String} body E-mail body
*
* @return {String} Mime folded DKIM-Signature string
*/
function generateDKIMHeader(domainName, keySelector, headerFieldNames, headers, body){
var canonicalizedBody = DKIMCanonicalizer.relaxedBody(body),
canonicalizedBodyHash = sha256(canonicalizedBody, "base64"),
canonicalizedHeaderData = DKIMCanonicalizer.relaxedHeaders(headers, headerFieldNames),
dkim;
if(hasUTFChars(domainName)){
domainName = toPunycode(domainName);
}
dkim = [
"v=1",
"a=rsa-sha256",
"c=relaxed/relaxed",
"d="+domainName,
"q=dns/txt",
"s="+keySelector,
"bh="+canonicalizedBodyHash,
"h="+canonicalizedHeaderData.fieldNames
].join("; ");
return mimelib.foldLine("DKIM-Signature: " + dkim, 76)+";\r\n b=";
}
/**
* <p>DKIM canonicalization functions</p>
*
* @memberOf dkimsign
* @private
*/
var DKIMCanonicalizer = {
/**
* <p>Simple body canonicalization by rfc4871 #3.4.3</p>
*
* @param {String} body E-mail body part
* @return {String} Canonicalized body
*/
simpleBody: function(body){
return (body || "").toString().replace(/(?:\r?\n|\r)*$/, "\r\n");
},
/**
* <p>Relaxed body canonicalization by rfc4871 #3.4.4</p>
*
* @param {String} body E-mail body part
* @return {String} Canonicalized body
*/
relaxedBody: function(body){
return (body || "").toString().
replace(/\r?\n|\r/g, "\n").
split("\n").
map(function(line){
return line.replace(/\s*$/, ""). //rtrim
replace(/\s+/g, " "); // only single spaces
}).
join("\n").
replace(/\n*$/, "\n").
replace(/\n/g, "\r\n");
},
/**
* <p>Relaxed headers canonicalization by rfc4871 #3.4.2 with filtering</p>
*
* @param {String} body E-mail headers part
* @return {String} Canonicalized headers
*/
relaxedHeaders: function(headers, fieldNames){
var includedFields = (fieldNames || "").toLowerCase().
split(":").
map(function(field){
return field.trim();
}),
headerFields = {},
headerLines = headers.split(/\r?\n|\r/),
line, i;
// join lines
for(i = headerLines.length-1; i>=0; i--){
if(i && headerLines[i].match(/^\s/)){
headerLines[i-1] += headerLines.splice(i,1);
}else{
line = DKIMCanonicalizer.relaxedHeaderLine(headerLines[i]);
// on multiple values, include only the first one (the one in the bottom of the list)
if(includedFields.indexOf(line.key) >= 0 && !(line.key in headerFields)){
headerFields[line.key] = line.value;
}
}
}
headers = [];
for(i = includedFields.length-1; i>=0; i--){
if(!headerFields[includedFields[i]]){
includedFields.splice(i,1);
}else{
headers.unshift(includedFields[i]+":"+headerFields[includedFields[i]]);
}
}
return {
headers: headers.join("\r\n")+"\r\n",
fieldNames: includedFields.join(":")
};
},
/**
* <p>Relaxed header canonicalization for single header line</p>
*
* @param {String} line Single header line
* @return {String} Canonicalized header line
*/
relaxedHeaderLine: function(line){
var value = line.split(":"),
key = (value.shift() || "").toLowerCase().trim();
value = value.join(":").replace(/\s+/g, " ").trim();
return {key: key, value: value};
}
};
module.exports.DKIMCanonicalizer = DKIMCanonicalizer;
/**
* <p>Generates a SHA-256 hash</p>
*
* @param {String} str String to be hashed
* @param {String} [encoding="hex"] Output encoding
* @return {String} SHA-256 hash in the selected output encoding
*/
function sha256(str, encoding){
var shasum = crypto.createHash('sha256');
shasum.update(str);
return shasum.digest(encoding || "hex");
}
/**
* <p>Detects if a string includes unicode symbols</p>
*
* @param {String} str String to be checked
* @return {String} true, if string contains non-ascii symbols
*/
function hasUTFChars(str){
var rforeign = /[^\u0000-\u007f]/;
return !!rforeign.test(str);
}
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