private InputStream readCipherSpecsAndUpdateHmac(InputStream underlyingInputStream, Mac hmac, CipherSession cipherSession) throws Exception { int cipherSpecCount = readByteAndUpdateHmac(underlyingInputStream, hmac); InputStream nestedCipherInputStream = underlyingInputStream; for (int i=0; i<cipherSpecCount; i++) { int cipherSpecId = readByteAndUpdateHmac(underlyingInputStream, hmac); CipherSpec cipherSpec = CipherSpecs.getCipherSpec(cipherSpecId); if (cipherSpec == null) { throw new IOException("Cannot find cipher spec with ID "+cipherSpecId); } byte[] salt = readAndUpdateHmac(underlyingInputStream, MultiCipherOutputStream.SALT_SIZE, hmac); byte[] iv = readAndUpdateHmac(underlyingInputStream, cipherSpec.getIvSize()/8, hmac); SecretKey secretKey = cipherSession.getReadSecretKey(cipherSpec, salt); nestedCipherInputStream = cipherSpec.newCipherInputStream(nestedCipherInputStream, secretKey.getEncoded(), iv); } return nestedCipherInputStream; }