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POHow do i decrypt a file in Android with AES?
 

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  1. POHow do i decrypt a file in Android with AES?
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    <p>I have a file (mp3) that i Encrypt, my intention is then to download this file to an android device and decrypt it, but during decryption i get an IOException:</p> <p><code>java.io.IOException: last block incomplete in decryption</code></p> <p>I am aware of the obvious security flaws in the following code, I'm just trying to get it to work first.</p> <p>Any help on this is appreciated and I am quite a newcomer to coding in general so excuse me in advance if this is a stupid question!</p> <p>Encryption class(Not done in Android, works):</p> <pre><code>public class EncryptFile { public static void main(String args[]) { if (args.length &lt; 1) { System.out.println("Usage: java EncryptFile &lt;file name&gt;"); System.exit(-1); } try { File aesFile = new File("encodedfile.enc"); FileInputStream fis; FileOutputStream fos; CipherInputStream cis; //Creation of Secret key String key = "mysecretkey"; int length=key.length(); if(length&gt;16 &amp;&amp; length!=16){ key=key.substring(0, 15); } if(length&lt;16 &amp;&amp; length!=16){ for(int i=0;i&lt;16-length;i++){ key=key+"0"; } } SecretKeySpec secretKey = new SecretKeySpec(key.getBytes(),"AES"); //Creation of Cipher objects Cipher encrypt =Cipher.getInstance("AES/CBC/PKCS5Padding"); byte[] aByte = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}; IvParameterSpec ivSpec = new IvParameterSpec(aByte); encrypt.init(Cipher.ENCRYPT_MODE, secretKey, ivSpec); try { fis = new FileInputStream(args[0]); cis = new CipherInputStream(fis,encrypt); // Write to the Encrypted file fos = new FileOutputStream(aesFile); byte[] b = new byte[8]; int i = cis.read(b); while (i != -1) { fos.write(b, 0, i); i = cis.read(b); } fos.flush(); fos.close(); cis.close(); fis.close(); } catch(IOException err) { System.out.println("Cannot open file!"); System.exit(-1); } } catch(Exception e){ e.printStackTrace(); } } </code></pre> <p>}</p> <p>Decryption (In Android device):</p> <pre><code> public class DecryptFile { public static File main(String args[], File encFile, Context context) { for (int i = 0; i &lt; args.length; i++) { Log.i("ARGS", args[i]); } try { File aesFile = new File(args[0]); aesFile= encFile; Log.d("AESFILELENGTH", "aes length: " + aesFile.length()); File aesFileBis = new File(context.getFilesDir(), args[0]); FileInputStream fis; FileOutputStream fos; CipherInputStream cis; //Creation of Secret key String key = "mysecretkey"; int length=key.length(); if(length&gt;16 &amp;&amp; length!=16){ key=key.substring(0, 15); } if(length&lt;16 &amp;&amp; length!=16){ for(int i=0;i&lt;16-length;i++){ key=key+"0"; } } SecretKeySpec secretKey = new SecretKeySpec(key.getBytes(),"AES"); //Creation of Cipher objects Cipher decrypt =Cipher.getInstance("AES/CBC/PKCS5Padding"); byte[] aByte = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}; IvParameterSpec ivSpec = new IvParameterSpec(aByte); decrypt.init(Cipher.DECRYPT_MODE, secretKey, ivSpec); // Open the Encrypted file fis = new FileInputStream(aesFile); cis = new CipherInputStream(fis, decrypt); // Write to the Decrypted file fos = new FileOutputStream(aesFileBis); try { byte[] mByte = new byte[8]; int i = cis.read(mByte); Log.i("MBYTE", "mbyte i: " + i); while (i != -1) { fos.write(mByte, 0, i); i = cis.read(mByte); } } catch (IOException e) { e.printStackTrace(); } fos.flush(); fos.close(); cis.close(); fis.close(); return aesFileBis; } catch(Exception e){ e.printStackTrace(); } return null; } } </code></pre>
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    1. USPontus Backlund
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      1. POHow do i decrypt a file in Android with AES?
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    2. VO
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    1. COpossible duplicate of [How to handle "last block incomplete in decryption"](http://stackoverflow.com/questions/4598873/how-to-handle-last-block-incomplete-in-decryption)
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      1. POHow do i decrypt a file in Android with AES?
      1. USSimon
    2. COCheck the length of the non-Android encrypted file you are producing. Compare it with the length of the encrypted file you are reading in Android. The two lengths should, obviously, be the same. If they are not then you probably have a file transfer problem, not a decryption problem.
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      1. POHow do i decrypt a file in Android with AES?
      1. USrossum
    3. COI checked the file length and the encrypted file is 2 bytes larger than the original file, but this is due to the padding right? I also did a byte[] mBytebase = Base64.encodeBase64(key.getBytes()); and used it in my SecretKeySpec based on the "duplicate". Nothing seems to help
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      1. POHow do i decrypt a file in Android with AES?
      1. USPontus Backlund
 

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