How would I go about this? I have code encrypting a file using AES/CBC/PKCS5Padding in Java and as I understand form this picture: 
Partial decryption should be possible having part of ciphertext used by preceding block and the key. I have not found any examples of this, though. Any help?
The decrypting code is as fallows:
//skip the IV (ivSize is 16 here) - IV was pretended to the stream during encryption
data.skip(ivSize);
//skip n blocks
int n = 2;
System.out.println("skipped: " + data.skip(n*16));
byte[] iv = new byte[ivSize];
//use next 16 bytes as IV
data.read(iv);
// Hashing key.
MessageDigest digest = MessageDigest.getInstance("SHA-256");
digest.update(encryptionKey.getBytes(StandardCharsets.UTF_8));
byte[] keyBytes = new byte[16];
System.arraycopy(digest.digest(), 0, keyBytes, 0, keyBytes.length);
Cipher cipher;
try {
cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
SecretKeySpec keySpec = new SecretKeySpec(keyBytes, "AES");
IvParameterSpec ivSpec = new IvParameterSpec(iv);
cipher.init(Cipher.DECRYPT_MODE, keySpec, ivSpec);
} catch (GeneralSecurityException e) {
throw new IOException(e);
}
CipherInputStream cis = new CipherInputStream(data, cipher);
try {
ByteStreams.copy(ByteStreams.limit(cis, limit), output);
} catch (IOException exception) {
// starting with java 8 the JVM wraps an IOException around a GeneralSecurityException
// it should be safe to swallow a GeneralSecurityException
if (!(exception.getCause() instanceof GeneralSecurityException)) {
throw exception;
}
log.warning(exception.getMessage());
} finally {
cis.close();
}
