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Diffstat (limited to 'security/manager/ssl/DER.sys.mjs')
| -rw-r--r-- | security/manager/ssl/DER.sys.mjs | 333 |
1 files changed, 333 insertions, 0 deletions
diff --git a/security/manager/ssl/DER.sys.mjs b/security/manager/ssl/DER.sys.mjs new file mode 100644 index 0000000000..3620cf9f29 --- /dev/null +++ b/security/manager/ssl/DER.sys.mjs @@ -0,0 +1,333 @@ +/* This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +// A minimal ASN.1 DER decoder. Supports input lengths up to 65539 (one byte for +// the outer tag, one byte for the 0x82 length-length indicator, two bytes +// indicating a contents length of 65535, and then the 65535 bytes of contents). +// Intended to be used like so: +// +// let bytes = <an array of bytes describing a SEQUENCE OF INTEGER>; +// let der = new DER.DERDecoder(bytes); +// let contents = new DER.DERDecoder(der.readTagAndGetContents(DER.SEQUENCE)); +// while (!contents.atEnd()) { +// let integerBytes = contents.readTagAndGetContents(DER.INTEGER); +// <... do something with integerBytes ...> +// } +// der.assertAtEnd(); +// +// For CHOICE, use readTLVChoice and pass an array of acceptable tags. +// The convenience function readBIT_STRING is provided to handle the unused bits +// aspect of BIT STRING. It returns an object that has the properties contents +// (an array of bytes consisting of the bytes making up the BIT STRING) and +// unusedBits (indicating the number of unused bits at the end). +// All other functions generally return an array of bytes or a single byte as +// appropriate. +// peekTag can be used to see if the next tag is an expected given tag. +// readTLV reads and returns an entire (tag, length, value) tuple (again +// returned as an array of bytes). +// +// NB: While DERDecoder must be given an array, it does not validate that each +// element in the array is an integer in the range [0, 255]. If the input to be +// decoded could conceivably violate this property, callers should perform this +// check before using DERDecoder. + +const UNIVERSAL = 0 << 6; +const CONSTRUCTED = 1 << 5; +const CONTEXT_SPECIFIC = 2 << 6; + +const INTEGER = UNIVERSAL | 0x02; // 0x02 +const BIT_STRING = UNIVERSAL | 0x03; // 0x03 +const NULL = UNIVERSAL | 0x05; // 0x05 +const OBJECT_IDENTIFIER = UNIVERSAL | 0x06; // 0x06 +const PrintableString = UNIVERSAL | 0x13; // 0x13 +const TeletexString = UNIVERSAL | 0x14; // 0x14 +const IA5String = UNIVERSAL | 0x16; // 0x16 +const UTCTime = UNIVERSAL | 0x17; // 0x17 +const GeneralizedTime = UNIVERSAL | 0x18; // 0x18 +const UTF8String = UNIVERSAL | 0x0c; // 0x0c +const SEQUENCE = UNIVERSAL | CONSTRUCTED | 0x10; // 0x30 +const SET = UNIVERSAL | CONSTRUCTED | 0x11; // 0x31 + +const ERROR_INVALID_INPUT = "invalid input"; +const ERROR_DATA_TRUNCATED = "data truncated"; +const ERROR_EXTRA_DATA = "extra data"; +const ERROR_INVALID_LENGTH = "invalid length"; +const ERROR_UNSUPPORTED_ASN1 = "unsupported asn.1"; +const ERROR_UNSUPPORTED_LENGTH = "unsupported length"; +const ERROR_INVALID_BIT_STRING = "invalid BIT STRING encoding"; + +/** Class representing a decoded BIT STRING. */ +class BitString { + /** + * @param {number} unusedBits the number of unused bits + * @param {number[]} contents an array of bytes comprising the BIT STRING + */ + constructor(unusedBits, contents) { + this._unusedBits = unusedBits; + this._contents = contents; + } + + /** + * Get the number of unused bits in the BIT STRING + * + * @returns {number} the number of unused bits + */ + get unusedBits() { + return this._unusedBits; + } + + /** + * Get the contents of the BIT STRING + * + * @returns {number[]} an array of bytes representing the contents + */ + get contents() { + return this._contents; + } +} + +/** Class representing DER-encoded data. Provides methods for decoding it. */ +class DERDecoder { + /** + * @param {number[]} bytes an array of bytes representing the encoded data + */ + constructor(bytes) { + // Reject non-array inputs. + if (!Array.isArray(bytes)) { + throw new Error(ERROR_INVALID_INPUT); + } + if (bytes.length > 65539) { + throw new Error(ERROR_UNSUPPORTED_LENGTH); + } + this._bytes = bytes; + this._cursor = 0; + } + + /** + * Asserts that the decoder is at the end of the given data. Throws an error + * if this is not the case. + */ + assertAtEnd() { + if (!this.atEnd()) { + throw new Error(ERROR_EXTRA_DATA); + } + } + + /** + * Determines whether or not the decoder is at the end of the given data. + * + * @returns {boolean} true if the decoder is at the end and false otherwise + */ + atEnd() { + return this._cursor == this._bytes.length; + } + + /** + * Reads the next byte of data. Throws if no more data is available. + * + * @returns {number} the next byte of data + */ + readByte() { + if (this._cursor >= this._bytes.length) { + throw new Error(ERROR_DATA_TRUNCATED); + } + let val = this._bytes[this._cursor]; + this._cursor++; + return val; + } + + /** + * Given the next expected tag, reads and asserts that the next tag is in fact + * the given tag. + * + * @param {number} expectedTag the expected next tag + */ + _readExpectedTag(expectedTag) { + let tag = this.readByte(); + if (tag != expectedTag) { + throw new Error(`unexpected tag: found ${tag} instead of ${expectedTag}`); + } + } + + /** + * Decodes and returns the length portion of an ASN.1 TLV tuple. Throws if the + * length is incorrectly encoded or if it describes a length greater than + * 65535 bytes. Indefinite-length encoding is not supported. + * + * @returns {number} the length of the value of the TLV tuple + */ + _readLength() { + let nextByte = this.readByte(); + if (nextByte < 0x80) { + return nextByte; + } + if (nextByte == 0x80) { + throw new Error(ERROR_UNSUPPORTED_ASN1); + } + if (nextByte == 0x81) { + let length = this.readByte(); + if (length < 0x80) { + throw new Error(ERROR_INVALID_LENGTH); + } + return length; + } + if (nextByte == 0x82) { + let length1 = this.readByte(); + let length2 = this.readByte(); + let length = (length1 << 8) | length2; + if (length < 256) { + throw new Error(ERROR_INVALID_LENGTH); + } + return length; + } + throw new Error(ERROR_UNSUPPORTED_LENGTH); + } + + /** + * Reads <length> bytes of data if available. Throws if less than <length> + * bytes are available. + * + * @param {number} length the number of bytes to read. Must be non-negative. + * @returns {number[]} the next <length> bytes of data + */ + readBytes(length) { + if (length < 0) { + throw new Error(ERROR_INVALID_LENGTH); + } + if (this._cursor + length > this._bytes.length) { + throw new Error(ERROR_DATA_TRUNCATED); + } + let bytes = this._bytes.slice(this._cursor, this._cursor + length); + this._cursor += length; + return bytes; + } + + /** + * Given an expected next ASN.1 tag, ensures that that tag is next and returns + * the contents of that tag. Throws if a different tag is encountered or if + * the data is otherwise incorrectly encoded. + * + * @param {number} tag the next expected ASN.1 tag + * @returns {number[]} the contents of the tag + */ + readTagAndGetContents(tag) { + this._readExpectedTag(tag); + let length = this._readLength(); + return this.readBytes(length); + } + + /** + * Returns the next byte without advancing the decoder. Throws if no more data + * is available. + * + * @returns {number} the next available byte + */ + _peekByte() { + if (this._cursor >= this._bytes.length) { + throw new Error(ERROR_DATA_TRUNCATED); + } + return this._bytes[this._cursor]; + } + + /** + * Given an expected tag, reads the next entire ASN.1 TLV tuple, asserting + * that the tag matches. + * + * @param {number} tag the expected tag + * @returns {number[]} an array of bytes representing the TLV tuple + */ + _readExpectedTLV(tag) { + let mark = this._cursor; + this._readExpectedTag(tag); + let length = this._readLength(); + // read the bytes so we know they're there (also to advance the cursor) + this.readBytes(length); + return this._bytes.slice(mark, this._cursor); + } + + /** + * Reads the next ASN.1 tag, length, and value and returns them as an array of + * bytes. + * + * @returns {number[]} an array of bytes representing the next ASN.1 TLV + */ + readTLV() { + let nextTag = this._peekByte(); + return this._readExpectedTLV(nextTag); + } + + /** + * Convenience function for decoding a BIT STRING. Reads and returns the + * contents of the expected next BIT STRING. Throws if the next TLV isn't a + * BIT STRING or if the BIT STRING is incorrectly encoded. + * + * @returns {BitString} the next BIT STRING + */ + readBIT_STRING() { + let contents = this.readTagAndGetContents(BIT_STRING); + if (contents.length < 1) { + throw new Error(ERROR_INVALID_BIT_STRING); + } + let unusedBits = contents[0]; + if (unusedBits > 7) { + throw new Error(ERROR_INVALID_BIT_STRING); + } + // Zero bytes of content but some amount of padding is invalid. + if (contents.length == 1 && unusedBits != 0) { + throw new Error(ERROR_INVALID_BIT_STRING); + } + return new BitString(unusedBits, contents.slice(1, contents.length)); + } + + /** + * Looks to see if the next ASN.1 tag is the expected given tag. + * + * @param {number} tag the expected next ASN.1 tag + * @returns {boolean} true if the next tag is the given one and false otherwise + */ + peekTag(tag) { + if (this._cursor >= this._bytes.length) { + return false; + } + return this._bytes[this._cursor] == tag; + } + + /** + * Given a list of possible next ASN.1 tags, returns the next TLV if the next + * tag is in the list. Throws if the next tag is not in the list or if the + * data is incorrectly encoded. + * + * @param {number[]} tagList the list of potential next tags + * @returns {number[]} the contents of the next TLV if the next tag is in + * <tagList> + */ + readTLVChoice(tagList) { + let tag = this._peekByte(); + if (!tagList.includes(tag)) { + throw new Error( + `unexpected tag: found ${tag} instead of one of ${tagList}` + ); + } + return this._readExpectedTLV(tag); + } +} + +export const DER = { + UNIVERSAL, + CONSTRUCTED, + CONTEXT_SPECIFIC, + INTEGER, + BIT_STRING, + NULL, + OBJECT_IDENTIFIER, + PrintableString, + TeletexString, + IA5String, + UTCTime, + GeneralizedTime, + UTF8String, + SEQUENCE, + SET, + DERDecoder, +}; |