here is an pure java routine for .db.crypt12 without bouncycastle, but only JDK.
public class Crypt12 {
public static void main(final String[] args) {
final String c12File = "1/msgstore.db.crypt12"; // input file
final String decryptedDbFile = "1/msgstore.db"; // sqlite3 db output file
final String keyFile = "1/key";
try {
final byte[] key; try(FileInputStream s = new FileInputStream(keyFile)) { key = s.readAllBytes(); }
final byte[] buf; try(FileInputStream s = new FileInputStream(c12File)) { buf = s.readAllBytes(); }
if(!Arrays.equals(key, 27, 78, buf, 0, 51)) { System.out.println("Wrong Key-File"); return; }
final int available = buf.length - 67 - 20; // 67 Byte Header + 20 byte footer
final Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
final GCMParameterSpec iv = new GCMParameterSpec(128, buf, 51, 16);
cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(key, 126, 32, "AES"), iv);
final int zipLen = cipher.doFinal(buf, 67, available, buf, 0);
final Inflater unzip = new Inflater(false);
try(FileOutputStream s = new FileOutputStream(decryptedDbFile)) {
unzip.setInput(buf, 0, zipLen);
final byte[] b = new byte[1024];
while(!unzip.needsInput()) {
final int l = unzip.inflate(b, 0, b.length);
if(l > 0) s.write(b, 0, l);
}
}
} catch (final Exception e) {
e.printStackTrace(System.out);
}
}
}