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

Question

The RSA public key:

pubkey = \'MIGfMA0GCSqGSIb3DQEBA3UAA4GNADCBiQKBgQC35eMaYoJXEoJt5HxarHkzDBEMU3qIWE0HSQ77CwP/8UbX07W2XKwngUyY4k6Hl2M/n9TOZMZsiBzer/fqV+QNPN1m9M94eU

Answer 1

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

1. 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:

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

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

    less exteralkey.pem
   

2. 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.