#5868 Display warning for incorrect pgp checksum

extension/chrome/elements/pgp_block.ts

@@ -110,7 +110,8 @@ export class PgpBlockView extends View {
     if (data?.separateQuotedContentAndRenderText) {
       this.quoteModule.separateQuotedContentAndRenderText(
         data.separateQuotedContentAndRenderText.decryptedContent,
-        data.separateQuotedContentAndRenderText.isHtml
+        data.separateQuotedContentAndRenderText.isHtml,
+        data.separateQuotedContentAndRenderText.isChecksumInvalid
       );
     }
     if (data?.setFrameColor) {

extension/chrome/elements/pgp_block_modules/pgp-block-quote-module.ts

@@ -9,7 +9,7 @@ import { Xss } from '../../../js/common/platform/xss.js';
 export class PgpBlockViewQuoteModule {
   public constructor(private view: PgpBlockView) {}
 
-  public separateQuotedContentAndRenderText = (decryptedContent: string, isHtml: boolean) => {
+  public separateQuotedContentAndRenderText = (decryptedContent: string, isHtml: boolean, isChecksumInvalid: boolean) => {
     if (isHtml) {
       const message = $('<div>').html(Xss.htmlSanitizeKeepBasicTags(decryptedContent)); // xss-sanitized
       let htmlBlockQuoteExists = false;
@@ -32,10 +32,10 @@ export class PgpBlockViewQuoteModule {
           message[0].removeChild(shouldBeQuoted[i]);
           quotedHtml += shouldBeQuoted[i].outerHTML;
         }
-        this.view.renderModule.renderContent(message.html(), false);
+        this.view.renderModule.renderContent(message.html(), false, isChecksumInvalid);
         this.appendCollapsedQuotedContentButton(quotedHtml, true);
       } else {
-        this.view.renderModule.renderContent(decryptedContent, false);
+        this.view.renderModule.renderContent(decryptedContent, false, isChecksumInvalid);
       }
     } else {
       const lines = decryptedContent.split(/\r?\n/);
@@ -62,7 +62,7 @@ export class PgpBlockViewQuoteModule {
         // only got quoted part, no real text -> show everything as real text, without quoting
         lines.push(...linesQuotedPart.splice(0, linesQuotedPart.length));
       }
-      this.view.renderModule.renderContent(Str.escapeTextAsRenderableHtml(lines.join('\n')), false);
+      this.view.renderModule.renderContent(Str.escapeTextAsRenderableHtml(lines.join('\n')), false, isChecksumInvalid);
       if (linesQuotedPart.join('').trim()) {
         this.appendCollapsedQuotedContentButton(linesQuotedPart.join('\n'));
       }

extension/chrome/elements/pgp_block_modules/pgp-block-render-module.ts

@@ -46,9 +46,11 @@ export class PgpBlockViewRenderModule {
     });
   };
 
-  public renderContent = (htmlContent: string, isErr: boolean) => {
+  public renderContent = (htmlContent: string, isErr: boolean, isChecksumInvalid = false) => {
     let contentWithLink = linkifyHtml(htmlContent);
-
+    if (isChecksumInvalid) {
+      contentWithLink = `<div class="pgp-invalid-checksum">${Lang.pgpBlock.invalidCheckSum}</div>${contentWithLink}}`;
+    }
     // Temporary workaround for an issue where 'cryptup_reply' divs are not being hidden when replying to all
     // messages from the FES. The root cause is that FES currently returns the body of
     // password message replies as 'text/plain', which does not hide the divs as intended.

extension/css/cryptup.css

@@ -1592,6 +1592,13 @@ td {
   align-items: center;
 }
 
+.pgp-invalid-checksum {
+  border-left: 3px solid #d18826;
+  color: #d18826;
+  margin: 10px 0;
+  padding-left: 5px;
+}
+
 .pgp_badge {
   opacity: 1;
   margin-bottom: 1em;

extension/js/common/core/crypto/key.ts

@@ -489,6 +489,60 @@ export class KeyUtil {
     return keys.map(k => ({ id: k.id, emails: k.emails, armored: KeyUtil.armor(k), family: k.family }));
   }
 
+  public static validateChecksum = (armoredText: string): boolean => {
+    const lines = armoredText.split('\n').map(l => l.trim());
+
+    // Filter out known non-data lines
+    const dataCandidates = lines.filter(line => line.length > 0 && !line.startsWith('-----') && !line.startsWith('Version:') && !line.startsWith('Comment:'));
+
+    // Find checksum line
+    const checksumIndex = dataCandidates.findIndex(line => line.startsWith('='));
+    if (checksumIndex === -1) return false;
+
+    const checksumLine = dataCandidates[checksumIndex].slice(1);
+    const dataLines = dataCandidates.slice(0, checksumIndex);
+
+    // Decode checksum
+    let providedBytes: string;
+    try {
+      providedBytes = atob(checksumLine);
+    } catch {
+      return false;
+    }
+    if (providedBytes.length !== 3) return false;
+
+    const providedCRC = (providedBytes.charCodeAt(0) << 16) | (providedBytes.charCodeAt(1) << 8) | providedBytes.charCodeAt(2);
+
+    // Attempt to decode all data lines (some may not be base64)
+    const decodedChunks: string[] = [];
+    for (const line of dataLines) {
+      try {
+        decodedChunks.push(atob(line));
+      } catch {
+        // Not a valid base64 line, skip it
+      }
+    }
+
+    if (decodedChunks.length === 0) return false;
+
+    const rawData = decodedChunks.join('');
+    const dataBytes = new Uint8Array([...rawData].map(c => c.charCodeAt(0)));
+
+    return KeyUtil.crc24(dataBytes) === providedCRC;
+  };
+
+  private static crc24 = (dataBytes: Uint8Array): number => {
+    let crc = 0xb704ce;
+    for (const dataByte of dataBytes) {
+      crc ^= dataByte << 16;
+      for (let j = 0; j < 8; j++) {
+        crc <<= 1;
+        if (crc & 0x1000000) crc ^= 0x1864cfb;
+      }
+    }
+    return crc & 0xffffff;
+  };
+
   private static getSortValue(pubinfo: PubkeyInfo): number {
     const expirationSortValue = typeof pubinfo.pubkey.expiration === 'undefined' ? Infinity : pubinfo.pubkey.expiration;
     // sort non-revoked first, then non-expired

extension/js/common/lang.ts

@@ -93,6 +93,8 @@ export const Lang = {
     cannotLocate: 'Could not locate this message.',
     brokenLink: 'It seems it contains a broken link.',
     pwdMsgAskSenderUsePubkey: 'This appears to be a password-protected message. Please ask the sender to encrypt messages for your Public Key instead.',
+    invalidCheckSum:
+      'Warning: Checksum mismatch detected.\nThis indicates the message may have been altered or corrupted during transmission.\nDecryption may still succeed, but verify the message source and integrity if possible.',
   },
   compose: {
     abortSending: 'A message is currently being sent. Closing the compose window may abort sending the message.\nAbort sending?',

extension/js/common/message-renderer.ts

@@ -521,7 +521,8 @@ export class MessageRenderer {
     sigResult: VerifyRes | undefined,
     renderModule: RenderInterface,
     retryVerification: (() => Promise<VerifyRes | undefined>) | undefined,
-    plainSubject: string | undefined
+    plainSubject: string | undefined,
+    isChecksumInvalid = false
   ): Promise<{ publicKeys?: string[] }> => {
     if (isEncrypted) {
       renderModule.renderEncryptionStatus('encrypted');
@@ -603,7 +604,7 @@ export class MessageRenderer {
       );
     }
     decryptedContent = this.clipMessageIfLimitExceeds(decryptedContent);
-    renderModule.separateQuotedContentAndRenderText(decryptedContent, isHtml);
+    renderModule.separateQuotedContentAndRenderText(decryptedContent, isHtml, isChecksumInvalid);
     await MessageRenderer.renderPgpSignatureCheckResult(renderModule, sigResult, Boolean(signerEmail), retryVerification);
     if (renderableAttachments.length) {
       renderModule.renderInnerAttachments(renderableAttachments, isEncrypted);
@@ -743,7 +744,8 @@ export class MessageRenderer {
         result.signature,
         renderModule,
         this.getRetryVerification(signerEmail, verificationPubs => MessageRenderer.decryptFunctionToVerifyRes(() => decrypt(verificationPubs))),
-        plainSubject
+        plainSubject,
+        !KeyUtil.validateChecksum(encryptedData.toString())
       );
     } else if (result.error.type === DecryptErrTypes.format) {
       if (fallbackToPlainText) {

extension/js/common/render-interface.ts

@@ -24,7 +24,7 @@ export interface RenderInterface extends RenderInterfaceBase {
   renderPassphraseNeeded(longids: string[]): void;
   renderErr(errBoxContent: string, renderRawMsg: string | undefined, errMsg?: string): void;
   renderInnerAttachments(attachments: TransferableAttachment[], isEncrypted: boolean): void;
-  separateQuotedContentAndRenderText(decryptedContent: string, isHtml: boolean): void;
+  separateQuotedContentAndRenderText(decryptedContent: string, isHtml: boolean, isChecksumInvalid: boolean): void;
   renderVerificationInProgress(): void;
   renderSignatureOffline(retry: () => void): void;
 }

extension/js/common/render-message.ts

@@ -23,7 +23,7 @@ export type MessageInfo = {
 export type RenderMessage = {
   done?: true;
   resizePgpBlockFrame?: true;
-  separateQuotedContentAndRenderText?: { decryptedContent: string; isHtml: boolean };
+  separateQuotedContentAndRenderText?: { decryptedContent: string; isHtml: boolean; isChecksumInvalid: boolean };
   renderText?: string;
   progressOperation?: { operationId: string; text: string; perc?: number; init?: boolean };
   setFrameColor?: 'green' | 'gray' | 'red';

extension/js/common/render-relay.ts

@@ -78,8 +78,8 @@ export class RenderRelay implements RenderInterface {
     this.relay({ resizePgpBlockFrame: true });
   };
 
-  public separateQuotedContentAndRenderText = (decryptedContent: string, isHtml: boolean) => {
-    this.relay({ separateQuotedContentAndRenderText: { decryptedContent, isHtml } });
+  public separateQuotedContentAndRenderText = (decryptedContent: string, isHtml: boolean, isChecksumInvalid: boolean) => {
+    this.relay({ separateQuotedContentAndRenderText: { decryptedContent, isHtml, isChecksumInvalid } });
   };
 
   public renderText = (text: string) => {

test/source/tests/decrypt.ts

@@ -1882,7 +1882,7 @@ XZ8r4OC6sguP/yozWlkG+7dDxsgKQVBENeG6Lw==
           browser,
           threadId,
           {
-            content: [expectedContent],
+            content: [expectedContent, 'Warning: Checksum mismatch detected'],
             encryption: 'encrypted',
           },
           authHdr