Using pycrypto, how to import a RSA public key and use it to encrypt a string?

13

votes

The RSA public key:

pubkey = 'MIGfMA0GCSqGSIb3DQEBA3UAA4GNADCBiQKBgQC35eMaYoJXEoJt5HxarHkzDBEMU3qIWE0HSQ77CwP/8UbX07W2XKwngUyY4k6Hl2M/n9TOZMZsiBzer/fqV+QNPN1m9M94eUm2gQgwkoRj5battRCaNJK/23GGpCsTQatJN8PZBhJBb2Vlsvw5lFrSdMT1R7vaz+2EeNR/FitFXwIDAQAB'

how to import it and use it to encrypt a string?

I tried the following code but RSA.construct() raises exception (TypeError: must be long, not str).

from Crypto.PublicKey import RSA
from Crypto.Util import asn1
from base64 import b64decode

keyDER = b64decode(pubkey)
seq = asn1.DerSequence()
seq.decode(keyDER)
keyPub = RSA.construct((seq[0], seq[1]))
print keyPub.encrypt('mysecret', 32)

Thanks.

pythonrsapycrypto

17

votes

I too had trouble with this. I got it working like this:

key = RSA.generate(2048)

binPrivKey = key.exportKey('DER')
binPubKey =  key.publickey().exportKey('DER')

privKeyObj = RSA.importKey(binPrivKey)
pubKeyObj =  RSA.importKey(binPubKey)

msg = "attack at dawn"
emsg = pubKeyObj.encrypt(msg, 'x')[0]
dmsg = privKeyObj.decrypt(emsg)

assert(msg == dmsg)

If you're writing to files, you may find it easier to deal with hex strings instead of binary strings. I'm using these helper functions a lot

def bin2hex(binStr):
    return binascii.hexlify(binStr)

def hex2bin(hexStr):
    return binascii.unhexlify(hexStr)

16

votes

from Crypto.PublicKey import RSA
from Crypto.Cipher import PKCS1_v1_5 as Cipher_PKCS1_v1_5
from base64 import b64decode,b64encode

pubkey = 'MIGfMA0GCSqGSIb3DQEBA3UAA4GNADCBiQKBgQC35eMaYoJXEoJt5HxarHkzDBEMU3qIWE0HSQ77CwP/8UbX07W2XKwngUyY4k6Hl2M/n9TOZMZsiBzer/fqV+QNPN1m9M94eUm2gQgwkoRj5battRCaNJK/23GGpCsTQatJN8PZBhJBb2Vlsvw5lFrSdMT1R7vaz+2EeNR/FitFXwIDAQAB'
msg = "test"
keyDER = b64decode(pubkey)
keyPub = RSA.importKey(keyDER)
cipher = Cipher_PKCS1_v1_5.new(keyPub)
cipher_text = cipher.encrypt(msg.encode())
emsg = b64encode(cipher_text)
print emsg

9

votes

By using:

RSA.importKey(externKey)

with parameter externKey look like the following:

You shouldn't b64decode the externKey and the string should start with "-----BEGIN PUBLIC KEY-----" and "-----END PUBLIC KEY-----".

4

votes

The method I ended up using based on a few answers here:

from Crypto.PublicKey import RSA
from Crypto.Cipher import PKCS1_v1_5 as Cipher_PKCS1_v1_5

def encrypt_data(data):
    with open("/path/to/public.pem", "rb") as k:
        key = RSA.importKey(k.read())

    cipher = Cipher_PKCS1_v1_5.new(key)
    return cipher.encrypt(data.encode())


def decrypt_data(data):
    with open("path/to/private.pem", "rb") as k:
        key = RSA.importKey(k.read())

    decipher = Cipher_PKCS1_v1_5.new(key)
    return decipher.decrypt(data, None).decode()


message = "hello world!"
encrypted = encrypt_data(message)
decrypted = decrypt_data(message)

2

votes

From the documentation

importKey(externKey, passphrase=None)
Import an RSA key (public or private half), encoded in standard form.

2

votes

thanks @user9527 vote up for you

that solved my problem

my env: win10x64 python3.6.4 pycrypto2.6.1

here's my code, encrypt end decrypt, the key was from someone's blog.(if U occured with "ValueError: RSA key format is not supported", check the key format, it should be warpped with some thing like "-----BEGIN XXXX KEY-----")

pubkey = """-----BEGIN PUBLIC KEY-----
...
-----END PUBLIC KEY-----"""

prvkey = """-----BEGIN RSA PRIVATE KEY-----
...
-----END RSA PRIVATE KEY-----"""

from Crypto.PublicKey import RSA

from Crypto.Cipher import PKCS1_v1_5 as Cipher_PKCS1_v1_5

msg = "test"
print("raw msg->", msg)
keyPub = RSA.importKey(pubkey) # import the public key
cipher = Cipher_PKCS1_v1_5.new(keyPub)
#print(cipher.encrypt.__doc__)
cipher_text = cipher.encrypt(msg.encode()) # now we have the cipher
print("cipher text->", cipher_text)


keyPriv = RSA.importKey(prvkey) # import the private key
cipher = Cipher_PKCS1_v1_5.new(keyPriv)
#print(cipher.decrypt.__doc__)
decrypt_text = cipher.decrypt(cipher_text, None).decode()
print("decrypted msg->", decrypt_text)
assert msg == decrypt_text # check that
print("test passed")

the output:

raw msg-> test
cipher text-> b'\xb0]\x1f@B\x8b\xb5\xbf\x891:\t4D\x80$\xc0y\xaa\xb4\x86t/|\xeaM%\xf06\x14,\x9e?\x86R\x83\xd72\xe5\xfdsr:\x99\xe7v\xd9]&\xbc\x85\xd3\x16\x80\x19q\xe7\xb1\x89\xff/\x12\xe5\xb3\x9cu\x1f\x04x\xa5\xdfl\xcd\xae_\xba\x1b\x97\x9fa\xcf9O\xbfB\xf6\xd1N\xf5|<\xbf^\x84R\xecSo\x9a*\xf7\x8d\x8e\xbe0Q\xcd\x14\x13\xf98x\xe7\xd8x\x19\xaf\x98\xefu\xa8\xb1\xd3\xfa\xf2N\xca\xb5'
decrypted msg-> test
test passed

2

votes

If you want to import an external key using RSA.importkey( ), you have two options:

Read key from file:

 file = open('external.pem','r')
 external_key = file.read()
 key = RSA.import_key(external_key)

and your external key format must be something like this:

In Linux (I don't know about Windows) you can check it by this command:

 less exteralkey.pem

If you wanna hardcode your key into your code, your key must be like this:

 pubkey = "-----BEGIN PUBLIC KEY-----\n\
 MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAsDcmhF1kqsMw9HAUc231\n\
 IEr3OwVwocSM4JPUGVSTBDcM9tGoflx8UoN4M9EJrdCcVicZEt709L13jhUxo/hX\n\
 jUDqyQ6U+zyOYhoSwQpHKju2bwn6HMC8iq/ZwNqRFiqa23O2L8WSjZq4J/U1wWZ9\n\
 Zh7f0E5w8GZDkngceQI8nBWFPSAeQNAh0b4Vy1SYKapPrvUJdS9LsT3V9B2k2Nm1\n\
 4lUOtfufpWP5xjoC3MwOxgBsPJsuqpe7sZddG4YzQi3IuMAcc+C/ms9mA7OX5yxt\n\
 xgU3tAIzzBHgvwn9vANNJPzJMaOcm9kKMVJYXLHfg37IfIk1oV+/3BxMQ26ErNcC\n\
 9wIDAQAB\n\
 -----END PUBLIC KEY-----"

then you can import it:

 key = RSA.importkey(pubkey)

Note: if you do not add "\n" to the end of each line of your RSA key the RSA.importkey( ) will raise an error:

RSA key format is not supported

Note 2: I used "\" to indicate that statement is continued on the next line.

0

votes

This worked for me. Python 3.8

ubuntu@ubuntu:~$ sudo pip3 list|grep crypto

cryptography 2.8

cryptography-vectors 2.8

pycrypto 2.6.1

from Crypto.PublicKey import RSA
from Crypto.Cipher import PKCS1_v1_5 as Cipher_PKCS1_v1_5

def encrypt_data(data):
    with open("/home/echague/.ssh/id_rsa.pub", "rb") as k:
        key_pub = RSA.importKey(k.read())

    cipher = Cipher_PKCS1_v1_5.new(key_pub)
    return cipher.encrypt(data.encode())


def decrypt_data(data):
    with open("/home/echague/.ssh/id_rsa", "rb") as k:
        key_priv = RSA.importKey(k.read())

    decipher = Cipher_PKCS1_v1_5.new(key_priv)
    return decipher.decrypt(data, None).decode()


message = "hello world!"
encrypted = encrypt_data(message)
decrypted = decrypt_data(encrypted)
print(message)
print(encrypted)
print(decrypted)

Using pycrypto, how to import a RSA public key and use it to encrypt a string?

8 Answers