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D7222.1768417655.diff
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diff --git a/lib/utils/pkcs7-padding.js b/lib/utils/pkcs7-padding.js
--- a/lib/utils/pkcs7-padding.js
+++ b/lib/utils/pkcs7-padding.js
@@ -30,6 +30,27 @@
superblockSizeBlocks: 40,
};
+/**
+ * Calculates length of the data padded with given padding configuration.
+ *
+ * @param {number} inputLength length of the unpadded input (in bytes)
+ * @param paddingConfiguration padding configuration
+ * @returns length of the padded input (in bytes)
+ */
+function calculatePaddedLength(
+ inputLength: number,
+ { blockSizeBytes, superblockSizeBlocks }: PaddingConfiguration = PKCS7_10KB,
+): number {
+ const pkcs7padding = blockSizeBytes - (inputLength % blockSizeBytes);
+ const pkcs7PaddedLen = inputLength + pkcs7padding;
+
+ const numBlocks = pkcs7PaddedLen / blockSizeBytes;
+ const paddingBlocks =
+ superblockSizeBlocks - (numBlocks % superblockSizeBlocks);
+
+ return pkcs7PaddedLen + paddingBlocks * blockSizeBytes;
+}
+
/**
* Pads the input using the extended PKCS#7 padding (superblock padding).
* The input is first padded using the standard PKCS#7 padding, and then
@@ -169,7 +190,7 @@
return unpaddedData;
}
-export { PKCS7_10KB, pad, unpad };
+export { PKCS7_10KB, pad, unpad, calculatePaddedLength };
// exported for testing purposes only
export const testing = {
diff --git a/lib/utils/pkcs7-padding.test.js b/lib/utils/pkcs7-padding.test.js
--- a/lib/utils/pkcs7-padding.test.js
+++ b/lib/utils/pkcs7-padding.test.js
@@ -1,7 +1,7 @@
// @flow
import type { PaddingConfiguration } from './pkcs7-padding';
-import { pad, unpad, testing } from './pkcs7-padding.js';
+import { pad, unpad, testing, calculatePaddedLength } from './pkcs7-padding.js';
const { pkcs7pad, pkcs7unpad, superblockPad, superblockUnpad } = testing;
@@ -213,6 +213,27 @@
});
});
+describe('calculatePaddingLength', () => {
+ it('should calculate the correct padding length', () => {
+ // we're using a 16 byte block size and 4 block superblocks (64 bytes total)
+ // let's say our data is 83 bytes long (1 full superblock + 19 bytes)
+ // we need to pad it to be equal to 2 superblocks (2 * 64 = 128 bytes)
+ // expected padding length is 128-83 = 45 bytes
+ const blockSizeBytes = 16;
+ const superblockSizeBlocks = 4;
+
+ const inputLength = 83;
+ const expectedPaddedLength = 128;
+
+ const calculatedLength = calculatePaddedLength(inputLength, {
+ blockSizeBytes,
+ superblockSizeBlocks,
+ });
+
+ expect(calculatedLength).toBe(expectedPaddedLength);
+ });
+});
+
function generateRandomData(length: number): Uint8Array {
const data = new Uint8Array(length);
for (let i = 0; i < length; i++) {

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