64 lines
2.3 KiB
JavaScript
64 lines
2.3 KiB
JavaScript
"use strict";
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/*
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Copyright 2023 The Sigstore Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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Object.defineProperty(exports, "__esModule", { value: true });
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exports.encodeLength = exports.decodeLength = void 0;
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const error_1 = require("./error");
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// Decodes the length of a DER-encoded ANS.1 element from the supplied stream.
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// https://learn.microsoft.com/en-us/windows/win32/seccertenroll/about-encoded-length-and-value-bytes
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function decodeLength(stream) {
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const buf = stream.getUint8();
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// If the most significant bit is UNSET the length is just the value of the
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// byte.
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if ((buf & 0x80) === 0x00) {
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return buf;
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}
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// Otherwise, the lower 7 bits of the first byte indicate the number of bytes
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// that follow to encode the length.
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const byteCount = buf & 0x7f;
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// Ensure the encoded length can safely fit in a JS number.
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if (byteCount > 6) {
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throw new error_1.ASN1ParseError('length exceeds 6 byte limit');
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}
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// Iterate over the bytes that encode the length.
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let len = 0;
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for (let i = 0; i < byteCount; i++) {
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len = len * 256 + stream.getUint8();
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}
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// This is a valid ASN.1 length encoding, but we don't support it.
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if (len === 0) {
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throw new error_1.ASN1ParseError('indefinite length encoding not supported');
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}
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return len;
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}
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exports.decodeLength = decodeLength;
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// Translates the supplied value to a DER-encoded length.
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function encodeLength(len) {
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if (len < 128) {
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return Buffer.from([len]);
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}
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// Bitwise operations on large numbers are not supported in JS, so we need to
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// use BigInts.
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let val = BigInt(len);
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const bytes = [];
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while (val > 0n) {
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bytes.unshift(Number(val & 255n));
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val = val >> 8n;
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}
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return Buffer.from([0x80 | bytes.length, ...bytes]);
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}
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exports.encodeLength = encodeLength;
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