Can anyone help me to reconvert im2uint16 back to image?

plaintextUnicodeVals = im2uint16(plaintext);
%display(plaintextUnicodeVals);
plaintextBytes = im2uint8(plaintextUnicodeVals);
display(plaintextBytes);

ciphertext = cipher.doFinal(plaintextBytes)'  %'
display(ciphertext);

how to convert back to image after decrypting cipher?

Answer 1

[Geoff Hayes]

Arya - it seems that you are using the Java cryptography cipher class (see https://docs.oracle.com/javase/7/docs/api/javax/crypto/Cipher.html) to encrypt your message. If we use RSA, which has a limit of 117 bytes for the plaintext message, then we could encrypt and decrypt as

import javax.crypto.Cipher;

% initialize the plaintext message
plaintext = 'I want to encrypt this message';

% initialize the cipher to encrypt
cipher  = Cipher.getInstance('RSA');
keygen  = java.security.KeyPairGenerator.getInstance('RSA');
keyPair = keygen.genKeyPair();
cipher.init(Cipher.ENCRYPT_MODE, keyPair.getPrivate());

% encrypt the message
ciphertext = cipher.doFinal(int8(plaintext));

% initialize the cipher to decrypt
cipher.init(Cipher.DECRYPT_MODE, keyPair.getPublic());

% decrypt the message
decryptedtext = char(uint8(cipher.doFinal(ciphertext)))'

Since you are encrypting an image, you may be using a different encryption algorithm (one that allows more than the 117 bytes for RSA).

[Arya Sebastian]

Thank you Mr.Geoff Hayes, I didn't know about the 117 bytes limit for RSA, could you please let me know a better algorithm or library function to encrypt and decrypt MRI images. Thanks again.

[Geoff Hayes]

Aria - I don't understand why you want to encrypt an MRI image. For what purpose?

[Geoff Hayes]

Arya's answer moved here

Sir, I am sending the MRI image as a part of my project In order to provide security,I have to use some better algorithms for encryption before transmitting the image.

[Geoff Hayes]

Arya - you may want to encrypt blocks of the images where a block is (say) 100 bytes. Then you could use the above code to encrypt the image.