CODEWITHSUNDEEP
pythongoogle-app-engineencryptionrsa
Horacio Molino
Horacio Molino

Reputation: 1

How to save an RSA key in GAE

I generate an RSA key:

random_generator  = Random.new().read
k1                = RSA.generate(1024,random_generator)

If I create a new key from k1 export all works:

export             = k1.exportKey() 
k2                 = RSA.importKey(export)

If I encrypt with k1 and decrypt with k2 all is fine.

I would like to save "export" and then use it to create a new key, k3, so that I can encrypt with k1 and decrypt with k3. No luck so far. This is what I have tried:

class SavedKey(db.Model):
    k       =    db.BlobProperty()
r = SavedKey()
    r.k = export
    r.put()

What I retrieve does not work:

retrieved =db.GqlQuery("Select * from SavedKey ").fetch(1000)[0]
retrieved = saved.k
k3 = RSA.importKey(retrieved)

"retrieved" is in the correct private key format but of different value than the original "export". k3 works for encryption and decryption, but encrypted by k1 of course does not decrypt with k3, which is what I am trying to achieve.

What am I doing wrong?

Upvotes: 0

Views: 72

Answers (1)

Alex Martelli
Alex Martelli

Reputation: 882281

What you're doing wrong is, you're retrieving the wrong entity. Think of

db.GqlQuery("Select * from SavedKey ").fetch(1000)[0]

as retrieving a "random" one of the SavedKey entities you have in the datastore. If instead you make sure you retrieve the actual one built from that export (hard to do, as your SavedKey model has no identifying property), everything will work fine.

Here's an example (using ndb as it makes little sense to keep using the old db):

class MainHandler(webapp2.RequestHandler):
    def get(self):
        random_generator = Random.new().read
        k1 = RSA.generate(1024, random_generator)
        export = k1.exportKey() 

        self.response.headers['Content-Type'] = 'text/plain'
        self.response.write(export)

        r = SavedKey()
        r.k = export
        rk = r.put() 

        retrieved = rk.get().k
        self.response.write(retrieved)
        k3 = RSA.importKey(retrieved)

        encrypted = k1.encrypt('four score and seven years ago', 0)
        decrypted = k3.decrypt(encrypted)
        self.response.write('\n' + decrypted)

...this will work just fine.

Upvotes: 3

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