encryption - How to encrypt and decrypt file for Android Kitkat and higher? -


i googling , testing solution while , far no success. there problem it. following code "working" (meaning not show error while running) on android kitkat , higher, decrypted files not readable. why?

final static byte[] iv = new byte[16];//added final static int buffer = 102400; final static string encryptiontype = "aes/cfb8/nopadding";//changed different type  static void encrypt(string password, file fileinput, file fileoutput) throws exception {      ivparameterspec ivparams = new ivparameterspec(iv);//added      fileinputstream fis = new fileinputstream(fileinput);     fileoutputstream fos = new fileoutputstream(fileoutput);      secretkeyspec sks = new secretkeyspec(password.getbytes("utf-8"), encryptiontype);      cipher cipher = cipher.getinstance(encryptiontype);     //cipher.init(cipher.encrypt_mode, sks);replaced     cipher.init(cipher.encrypt_mode, sks, ivparams);     cipheroutputstream cos = new cipheroutputstream(fos, cipher);      int b;     byte[] d = new byte[buffer];     while ((b = fis.read(d)) != -1) {         cos.write(d, 0, b);     }      cos.flush();     cos.close();     fis.close(); }  static void decrypt(string password, file fileinput, file fileoutput) throws exception {      ivparameterspec ivparams = new ivparameterspec(iv);//added      fileinputstream fis = new fileinputstream(fileinput);     fileoutputstream fos = new fileoutputstream(fileoutput);      secretkeyspec sks = new secretkeyspec(password.getbytes("utf-8"), encryptiontype);      cipher cipher = cipher.getinstance(encryptiontype);     //cipher.init(cipher.encrypt_mode, sks);replaced     cipher.init(cipher.decrypt_mode, sks, ivparams);     cipherinputstream cis = new cipherinputstream(fis, cipher);      int b;     byte[] d = new byte[buffer];     while ((b = cis.read(d)) != -1) {         fos.write(d, 0, b);     }      fos.flush();     fos.close();     cis.close(); }

edit: after changed type "aes/cfb8/nopadding", seems ok, there no error in process, decrypted file not readable.

the problem in decrypt method caused line:

cipher.init(cipher.encrypt_mode, sks);

the mode needs cipher.decrypt_mode, line should be

cipher.init(cipher.decrypt_mode, sks);

other issues use of long obsolete desede algorithm, lack of iv generation , handling, absence of password-based key derivation algorithm, , lack of mac on ciphertext. correctly using aes gcm mode proper nonce generation , handling, , use of pbkdf2 (which available on android , oracle java) represent significant improvements.

you don't supply iv, 1 generated automatically. must find way transmit iv recipient. typically iv/nonce prepending ciphertext , stripped off recipient in order decrypt data. cipherinputstream/cipheroutputstream not you, must on own.


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