Support multi-chunk encrypted uploads in web interface

src/core/passwords.cpp

@@ -172,6 +172,44 @@ String encryptString(String &plaintext, const String &password_str) {
     return out;
 }
 
+String encryptFileHeader() {
+    // Same header encryptString() writes, up to (and including) the "Data: " prefix.
+    // The hex payload that follows may be appended incrementally across chunks.
+    String out = "Filetype: Bruce Encrypted File\nVersion: 1\n";
+    out += "Algo: XOR\n";
+    out += "KeyDerivationAlgo: MD5\n";
+    out += "KeyDerivationPasses: 10\n";
+    out += "Data: ";
+    return out;
+}
+
+String encryptChunkToHex(const uint8_t *data, size_t len, const String &password_str, size_t streamOffset) {
+    // Derive the same 16-byte key xorEncryptDecryptMD5() uses (MD5 of the password, 10
+    // passes), so a chunk-encrypted file decrypts identically to a single-shot one.
+    MD5Builder md5;
+    String hash = password_str;
+    for (int i = 0; i < 10; i++) {
+        md5.begin();
+        md5.add(hash);
+        md5.calculate();
+    }
+    uint8_t md5Hash[16];
+    md5.getBytes(md5Hash);
+
+    // Fixed-width "XX " per byte: the reader parses the Data line in 3-char groups, so
+    // every byte must be two uppercase hex digits followed by a separator.
+    static const char hexDigits[] = "0123456789ABCDEF";
+    String out;
+    out.reserve(len * 3);
+    for (size_t i = 0; i < len; i++) {
+        uint8_t b = data[i] ^ md5Hash[(streamOffset + i) % 16];
+        out += hexDigits[(b >> 4) & 0x0F];
+        out += hexDigits[b & 0x0F];
+        out += ' ';
+    }
+    return out;
+}
+
 /* OLD:
 String decryptString(String& cypertext, const String& password_str)
 

src/core/passwords.h

@@ -6,6 +6,13 @@
 
 String encryptString(String &plaintext, const String &password_str);
 
+// Streaming helpers for chunked encryption (e.g. web uploads). The XOR keystream is
+// position-based, so a file can be encrypted chunk by chunk as long as each chunk knows
+// its absolute offset in the plaintext. encryptFileHeader() emits the header once,
+// ending with "Data: "; encryptChunkToHex() appends the hex bytes for one chunk.
+String encryptFileHeader();
+String encryptChunkToHex(const uint8_t *data, size_t len, const String &password_str, size_t streamOffset);
+
 String decryptString(String &cypertext, const String &password_str);
 
 String readDecryptedFile(FS &fs, String filepath);

src/core/wifi/webInterface.cpp

@@ -238,20 +238,20 @@ void handleUpload(
                 // Serial.println("Failed to open file for writing: " + uploadFolder + "/" + filename);
                 goto RETRY;
             }
+            if (request->hasArg("password") && request->_tempFile) {
+                // Write the encrypted-file header once; the hex payload is streamed per chunk.
+                String header = encryptFileHeader();
+                request->_tempFile.write((const uint8_t *)header.c_str(), header.length());
+            }
         }
 
         if (len) {
             if (request->hasArg("password")) {
-                // encryption requested
-                static int chunck_no = 0;
-                if (chunck_no != 0) {
-                    // TODO: handle multiple chunks
-                    request->send(404, "text/html", "file is too big");
-                    return;
-                } else chunck_no += 1;
+                // Encrypt this chunk incrementally. The XOR keystream is position-based, so
+                // `index` (the chunk's offset in the plaintext) keeps it continuous across
+                // chunks without buffering the whole file in RAM.
                 String enc_password = request->arg("password");
-                String plaintext = String((char *)data).substring(0, len);
-                String cyphertxt = encryptString(plaintext, enc_password);
+                String cyphertxt = encryptChunkToHex(data, len, enc_password, index);
                 if (cyphertxt == "") { return; }
                 if (request->_tempFile)
                     request->_tempFile.write((const uint8_t *)cyphertxt.c_str(), cyphertxt.length());
@@ -260,6 +260,8 @@ void handleUpload(
             }
         }
         if (final) {
+            // Terminate the encrypted Data line before closing, matching encryptString().
+            if (request->hasArg("password") && request->_tempFile) request->_tempFile.write((const uint8_t *)"\n", 1);
             // close the file handle as the upload is now done
             if (request->_tempFile) request->_tempFile.close();
         }