70 lines
1.9 KiB
JavaScript
70 lines
1.9 KiB
JavaScript
'use strict';
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//
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// A dumbed-down, minimal ASN.1 packer
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//
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// Almost every ASN.1 type that's important for CSR
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// can be represented generically with only a few rules.
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var ASN1 = function ASN1(/*type, hexstrings...*/) {
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var args = Array.prototype.slice.call(arguments);
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var typ = args.shift();
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var str = args.join('').replace(/\s+/g, '').toLowerCase();
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var len = (str.length/2);
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var lenlen = 0;
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var hex = typ;
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// We can't have an odd number of hex chars
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if (len !== Math.round(len)) {
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throw new Error("invalid hex");
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}
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// The first byte of any ASN.1 sequence is the type (Sequence, Integer, etc)
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// The second byte is either the size of the value, or the size of its size
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// 1. If the second byte is < 0x80 (128) it is considered the size
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// 2. If it is > 0x80 then it describes the number of bytes of the size
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// ex: 0x82 means the next 2 bytes describe the size of the value
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// 3. The special case of exactly 0x80 is "indefinite" length (to end-of-file)
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if (len > 127) {
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lenlen += 1;
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while (len > 255) {
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lenlen += 1;
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len = len >> 8;
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}
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}
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if (lenlen) { hex += ASN1.numToHex(0x80 + lenlen); }
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return hex + ASN1.numToHex(str.length/2) + str;
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};
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// The Integer type has some special rules
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ASN1.UInt = function UINT() {
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var str = Array.prototype.slice.call(arguments).join('');
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var first = parseInt(str.slice(0, 2), 16);
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// If the first byte is 0x80 or greater, the number is considered negative
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// Therefore we add a '00' prefix if the 0x80 bit is set
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if (0x80 & first) { str = '00' + str; }
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return ASN1('02', str);
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};
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// The Bit String type also has a special rule
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ASN1.BitStr = function BITSTR() {
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var str = Array.prototype.slice.call(arguments).join('');
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// '00' is a mask of how many bits of the next byte to ignore
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return ASN1('03', '00' + str);
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};
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ASN1.numToHex = function (d) {
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d = d.toString(16);
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if (d.length % 2) {
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return '0' + d;
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}
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return d;
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};
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module.exports = ASN1;
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