Symmetric Key and Public Key Encryption

Author: itfreetraining
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Modern day encryption is performed in two different ways. Check out http://YouTube.com/ITFreeTraining or http://itfreetraining.com for more of our always free training videos. Using the same key or using a pair of keys called the public and private keys. This video looks at how these systems work and how they can be used together to perform encryption. Download the PDF handout http://itfreetraining.com/Handouts/Ce... Encryption Types Encryption is the process of scrambling data so it cannot be read without a decryption key. Encryption prevents data being read by a 3rd party if it is intercepted by a 3rd party. The two encryption methods that are used today are symmetric and public key encryption. Symmetric Key Symmetric key encryption uses the same key to encrypt data as decrypt data. This is generally quite fast when compared with public key encryption. In order to protect the data, the key needs to be secured. If a 3rd party was able to gain access to the key, they could decrypt any data that was encrypt with that data. For this reason, a secure channel is required to transfer the key if you need to transfer data between two points. For example, if you encrypted data on a CD and mail it to another party, the key must also be transferred to the second party so that they can decrypt the data. This is often done using e-mail or the telephone. In a lot of cases, sending the data using one method and the key using another method is enough to protect the data as an attacker would need to get both in order to decrypt the data. Public Key Encryption This method of encryption uses two keys. One key is used to encrypt data and the other key is used to decrypt data. The advantage of this is that the public key can be downloaded by anyone. Anyone with the public key can encrypt data that can only be decrypted using a private key. This means the public key does not need to be secured. The private key does need to be keep in a safe place. The advantage of using such a system is the private key is not required by the other party to perform encryption. Since the private key does not need to be transferred to the second party there is no risk of the private key being intercepted by a 3rd party. Public Key encryption is slower when compared with symmetric key so it is not always suitable for every application. The math used is complex but to put it simply it uses the modulus or remainder operator. For example, if you wanted to solve X mod 5 = 2, the possible solutions would be 2, 7, 12 and so on. The private key provides additional information which allows the problem to be solved easily. The math is more complex and uses much larger numbers than this but basically public and private key encryption rely on the modulus operator to work. Combing The Two There are two reasons you want to combine the two. The first is that often communication will be broken into two steps. Key exchange and data exchange. For key exchange, to protect the key used in data exchange it is often encrypted using public key encryption. Although slower than symmetric key encryption, this method ensures the key cannot accessed by a 3rd party while being transferred. Since the key has been transferred using a secure channel, a symmetric key can be used for data exchange. In some cases, data exchange may be done using public key encryption. If this is the case, often the data exchange will be done using a small key size to reduce the processing time. The second reason that both may be used is when a symmetric key is used and the key needs to be provided to multiple users. For example, if you are using encryption file system (EFS) this allows multiple users to access the same file, which includes recovery users. In order to make this possible, multiple copies of the same key are stored in the file and protected from being read by encrypting it with the public key of each user that requires access. References "Public-key cryptography" http://en.wikipedia.org/wiki/Public-k... "Encryption" http://en.wikipedia.org/wiki/Encryption

Comments

  1. Thanks a lot
  2. Suppose of an account with one user name and multiple one-time password (exactly like crypto card).

    Lets suppose I have given ID (which is same everytime) and password ( which vary every time). Now my question is, how they verify that this password belongs to the same user ID. If a crypto card can generate over millions of password for a particular ID. Is it mean that there are millions of passwords stored in the server for that particular ID ?
  3. 6-7 min is enough
  4. Why should you use Public Key encryption when the Hacker does not know whether the message being sent is Encrypted or not. Further, why should the hacker always assume that the message being sent is always encrypted ? Any message could always be encrypted to form an understandable sentence in any Language which could mean something other than the intended message. So what's the big deal ?
  5. Something that I've never quite comprehended about asymmetric cryptography is how any message sent by the entity with the private key can be seen as secure?
    What I mean by this is that since anyone with the corresponding public key can decrypt what has been encrypted with the private key, it's not secure at all? An example of this would be if a server uses its private key to encrypt a message containing a user's new password for a website. An attacker could then use his/her public key used by that server to decrypt that message.

    What am I missing here? :)
  6. thanks a lot ... it was very useful
    جزاك الله خير
  7. what do you mean by key...what is this key
  8. anybody who gives a "dislike", would you please explain what is wrong with these fabulous vids?
  9. Wrong.
  10. nice job, could you please help me by IBC(identity based cryptography)? thanks
  11. can u guide me how to make an android application to encrypt videos
  12. Perfect Explanation Thanks very much
  13. at last.... i finally got this.
  14. I think I get it now. Can anyone vouch if this simple way to explain it is accurate? ----------

    Think of public keys as means to encrypt data, and private keys as a way to decrypt data. They are generated in pairs and go together. A client asks for the server to store a copy of its public key on the server (adding its public key to authrorized_keys file)

    When that client requests permission to the server, the server generates a random id, password, or token that the client will have to decrypt in order to "pass". The server encrypts/hashes this random password using the client's own public key and sends it back. Along with that, the server generates a private/public keypair of its own and sends the public key back to the client also.

    The client has the right private key to decrypt the password the server encypted and sent back, and does so. Now the client must send back the answer to the password to the server for verification, but do it securely. So it encrypts the password using the public key the server sent with with the original challenge, and sends to server.

    The server still has the private key it generated matching this public key, decrypts the password sent, and verifies it matches the random passord it generated for the request. At this point, they could/do continue to use this password as a common private "symmetric" key in order to be able to send data back and forth securely and quickly (common private key is faster).
  15. thanks a lot! ;)
  16. thanks! this will help me pass my exam.. wish me luck🙏🏼
  17. It seems to me you're trying to make it too complex. Take two identical dictionaries give every defined word a number than use a system with say! with 10,000 or 10,000,000 single individual digit. Give every number or word its own individual digit after that your options are almost endless.
  18. Thank you for this video, I understood this more then i understood my lecturer
  19. Thank you.
  20. Very well explained. Thank you.