ch9_encrypt_blob.py

ch9_encrypt_blob.py

#ch9_encrypt_blob.py
from Crypto.PublicKey import RSA
from Crypto.Cipher import PKCS1_OAEP
import zlib
import base64

#Our Encryption Function
def encrypt_blob(blob, public_key):
    #Import the Public Key and use for encryption using PKCS1_OAEP
    rsa_key = RSA.importKey(public_key)
    rsa_key = PKCS1_OAEP.new(rsa_key)

    #compress the data first
    blob = zlib.compress(blob)

    #In determining the chunk size, determine the private key length used in bytes
    #and subtract 42 bytes (when using PKCS1_OAEP). The data will be in encrypted
    #in chunks
    chunk_size = 470
    offset = 0
    end_loop = False
    encrypted =  ""

    while not end_loop:
        #The chunk
        chunk = blob[offset:offset + chunk_size]

        #If the data chunk is less then the chunk size, then we need to add
        #padding with " ". This indicates the we reached the end of the file
        #so we end loop here
        if len(chunk) % chunk_size != 0:
            end_loop = True
            chunk += " " * (chunk_size - len(chunk))

        #Append the encrypted chunk to the overall encrypted file
        encrypted += rsa_key.encrypt(chunk)

        #Increase the offset by chunk size
        offset += chunk_size

    #Base 64 encode the encrypted file
    return base64.b64encode(encrypted)

#Use the public key for encryption
fd = open("public_key.pem", "rb")
public_key = fd.read()
fd.close()

#Our candidate file to be encrypted
fd = open("img.jpg", "rb")
unencrypted_blob = fd.read()
fd.close()

encrypted_blob = encrypt_blob(unencrypted_blob, public_key)

#Write the encrypted contents to a file
fd = open("encrypted_img.jpg", "wb")
fd.write(encrypted_blob)
fd.close()

I got the same error and I didnt understand why

Any idea to solve this error

Traceback (most recent call last):
  File ".......py", line 288, in <module>
    encrypted_blob = encrypt_blob(html.encode('utf-8'), private_key.exportKey(format='PEM'))
  File ".......py", line 170, in encrypt_blob
    encrypted += rsa_key.encrypt(chunk)
  File "...../python3.6/site-packages/Crypto/Cipher/PKCS1_OAEP.py", line 115, in encrypt
    raise ValueError("Plaintext is too long.")
ValueError: Plaintext is too long.

If for some reason it would be relevant for others in the future... In Python3 you cannot convert bytes object to str implicitly.
So basically to solve that error about "concatenate str (not "bytes") to str", you must declare the variables as bytes

1. encrypted = b""
2. chunk += b" " * (chunk_size - len(chunk))