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Edit File: ecdsa-sig-formatter.js

'use strict';

var Buffer = require('safe-buffer').Buffer;

var getParamBytesForAlg = require('./param-bytes-for-alg');

var MAX_OCTET = 0x80,
	CLASS_UNIVERSAL = 0,
	PRIMITIVE_BIT = 0x20,
	TAG_SEQ = 0x10,
	TAG_INT = 0x02,
	ENCODED_TAG_SEQ = (TAG_SEQ | PRIMITIVE_BIT) | (CLASS_UNIVERSAL << 6),
	ENCODED_TAG_INT = TAG_INT | (CLASS_UNIVERSAL << 6);

function base64Url(base64) {
	return base64
		.replace(/=/g, '')
		.replace(/\+/g, '-')
		.replace(/\//g, '_');
}

function signatureAsBuffer(signature) {
	if (Buffer.isBuffer(signature)) {
		return signature;
	} else if ('string' === typeof signature) {
		return Buffer.from(signature, 'base64');
	}

throw new TypeError('ECDSA signature must be a Base64 string or a Buffer');
}

function derToJose(signature, alg) {
	signature = signatureAsBuffer(signature);
	var paramBytes = getParamBytesForAlg(alg);

// the DER encoded param should at most be the param size, plus a padding
	// zero, since due to being a signed integer
	var maxEncodedParamLength = paramBytes + 1;

var inputLength = signature.length;

var offset = 0;
	if (signature[offset++] !== ENCODED_TAG_SEQ) {
		throw new Error('Could not find expected "seq"');
	}

var seqLength = signature[offset++];
	if (seqLength === (MAX_OCTET | 1)) {
		seqLength = signature[offset++];
	}

if (inputLength - offset < seqLength) {
		throw new Error('"seq" specified length of "' + seqLength + '", only "' + (inputLength - offset) + '" remaining');
	}

if (signature[offset++] !== ENCODED_TAG_INT) {
		throw new Error('Could not find expected "int" for "r"');
	}

var rLength = signature[offset++];

if (inputLength - offset - 2 < rLength) {
		throw new Error('"r" specified length of "' + rLength + '", only "' + (inputLength - offset - 2) + '" available');
	}

if (maxEncodedParamLength < rLength) {
		throw new Error('"r" specified length of "' + rLength + '", max of "' + maxEncodedParamLength + '" is acceptable');
	}

var rOffset = offset;
	offset += rLength;

if (signature[offset++] !== ENCODED_TAG_INT) {
		throw new Error('Could not find expected "int" for "s"');
	}

var sLength = signature[offset++];

if (inputLength - offset !== sLength) {
		throw new Error('"s" specified length of "' + sLength + '", expected "' + (inputLength - offset) + '"');
	}

if (maxEncodedParamLength < sLength) {
		throw new Error('"s" specified length of "' + sLength + '", max of "' + maxEncodedParamLength + '" is acceptable');
	}

var sOffset = offset;
	offset += sLength;

if (offset !== inputLength) {
		throw new Error('Expected to consume entire buffer, but "' + (inputLength - offset) + '" bytes remain');
	}

var rPadding = paramBytes - rLength,
		sPadding = paramBytes - sLength;

var dst = Buffer.allocUnsafe(rPadding + rLength + sPadding + sLength);

for (offset = 0; offset < rPadding; ++offset) {
		dst[offset] = 0;
	}
	signature.copy(dst, offset, rOffset + Math.max(-rPadding, 0), rOffset + rLength);

offset = paramBytes;

for (var o = offset; offset < o + sPadding; ++offset) {
		dst[offset] = 0;
	}
	signature.copy(dst, offset, sOffset + Math.max(-sPadding, 0), sOffset + sLength);

dst = dst.toString('base64');
	dst = base64Url(dst);

return dst;
}

function countPadding(buf, start, stop) {
	var padding = 0;
	while (start + padding < stop && buf[start + padding] === 0) {
		++padding;
	}

var needsSign = buf[start + padding] >= MAX_OCTET;
	if (needsSign) {
		--padding;
	}

return padding;
}

function joseToDer(signature, alg) {
	signature = signatureAsBuffer(signature);
	var paramBytes = getParamBytesForAlg(alg);

var signatureBytes = signature.length;
	if (signatureBytes !== paramBytes * 2) {
		throw new TypeError('"' + alg + '" signatures must be "' + paramBytes * 2 + '" bytes, saw "' + signatureBytes + '"');
	}

var rPadding = countPadding(signature, 0, paramBytes);
	var sPadding = countPadding(signature, paramBytes, signature.length);
	var rLength = paramBytes - rPadding;
	var sLength = paramBytes - sPadding;

var rsBytes = 1 + 1 + rLength + 1 + 1 + sLength;

var shortLength = rsBytes < MAX_OCTET;

var dst = Buffer.allocUnsafe((shortLength ? 2 : 3) + rsBytes);

return dst;
}

module.exports = {
	derToJose: derToJose,
	joseToDer: joseToDer
};

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