Whether a bit or bit key is used depends on the encryption capabilities of both the server and the client software. SSL Certificates do not dictate what key size is used. Since asymmetric keys are bigger than symmetric keys, data that is encrypted asymmetrically is tougher to crack than data that is symmetrically encrypted. However, this does not mean that asymmetric keys are better.
Rather than being compared by their size, these keys should compared by the following properties: computational burden and ease of distribution. Symmetric keys are smaller than asymmetric, so they require less computational burden. However, symmetric keys also have a major disadvantage—especially if you use them for securing data transfers.
Because the same key is used for symmetric encryption and decryption, both you and the recipient need the key. However, if you have to send the key to a user halfway around the world a more likely scenario you need to worry about data security.
As long as you keep your private key secret, no one can decrypt your messages. You can distribute the corresponding public key without worrying who gets it. Anyone who has the public key can encrypt data, but only the person with the private key can decrypt it. Public Key Infrastructure PKI is the set of hardware, software, people, policies, and procedures that are needed to create, manage, distribute, use, store, and revoke digital certificates. PKI uses a hybrid cryptosystem and benefits from using both types of encryption.
The session key that the server and the browser create during the SSL Handshake is symmetric. This is explained further in the diagram below. With asymmetric encryption it is computationally easy to generate public and private keys, encrypt messages with the public key, and decrypt messages with the private key. However, it is extremely difficult or impossible for anyone to derive the private key based only on the public key.
RSA is based on the presumed difficulty of factoring large integers integer factorization. Full decryption of an RSA ciphertext is thought to be infeasible on the assumption that no efficient algorithm exists for integer factorization. A user of RSA creates and then publishes the product of two large prime numbers, along with an auxiliary value, as their public key.
Hmm I don't get why a certificate vendor talks about bit encryption. The symmetric encryption used by SSL is completely independent from the certificate. CodesInChaos: I agree, but maybe it is useful? Given the accepted answer below, my question is how would the client know to generate a random bit key? Why not ? If the server plays a role in the client's decision, then I can understand why the vendor would display this info.
Gilles I think that question is asking more about the bit encoding of keys, whereas I believe this one is about the difference between the types of keys.
Show 1 more comment. Active Oldest Votes. Improve this answer. Community Bot 1. Thomas Pornin Thomas Pornin k 57 57 gold badges silver badges bronze badges. Thank you! Can you clarify this part: "the client generates a random bit key"? In this case, the client is the browser? If so, does the ad mean to say that the root encryption is for the handshake portion and the bit is for the data encryption?
Hope I'm getting this. Ignore that question - I get it now. I combined your answer with the one in this post: security. Add a comment. Great info! However, wouldn't the tougher algorithm imply a greater level of security? I'm referring this part in your answer, "That said, because the algorithm is based on something that is simply really hard to figure out but is solvable , it is less secure than a symmetric algorithm based on a shared secret more on that later.
JohnJ - The problem is that it is solvable. A symmetric algorithm based on a shared secret key does not publicly provide the information necessary to solve it. There are some tricks that can be used to make more educated guesses, but it does not rely on a problem being hard to solve. If anyone ever came up with a way to factor very large primes quickly however for example, through quantum computing , RSA would immediately be broken and useless because the information shares is mathematically enough to determine the plaintext.
To clarify further, RSA is the asymmetric, bit algorithm, while the symmetric is the bit portion. Most of the attacks against symmetric encryption involve looking for either a known plaintext the thing being encrypted or patterns that result due to poor key selection or a problem in the underlying algorithm, but that is all based on analysis of the cyphertext as opposed to analysis of the key itself since the key is unavailable.
The inherent weakness in asymmetric cryptography is that the public key must be related to the private key and thus the private key can be derived. Thus the security of the asymmetric algorithm is dependent entirely on how hard it is to solve for the private key given the public one. There is no "challenge" "encrypted with private key" which is not an accurate description of signing anyway; there are dozens of questions about that.
For DHE and ECDHE key exchanges as described by Bruno, but not pure-RSA you and Thomas describe, the server adds a signature to the ServerKeyExchange message, whose contents are neither chosen nor echoed by the client, and which is after the server cert really chain is sent and presumably validated. Just to add some details to the existing answers This falls in two categories excluding anonymous key exchange : RSA key exchange e.
DH E key exchange e. The server signs its DH parameters and the client verifies the signature against the public key in the server certificate. In all versions of the TLS protocol, the certificate plays a very specific role: it is used when validating the hostname of the website and facilitates the creation of a session key that is used to protect the data in transit.
This means that the strength of the session key is at least as important as the certificate's key in protecting your data. The cipher suite also defines the method used to establish the session key. When a key agreement mechanism that provides FS is in use, a compromised key represented in the certificate cannot be used to recreate old session keys. Even if the encrypted TLS data is stored for a long time, cracking the certificate's key will not allow the data to be compromised.
A bit RSA key provides bit of security. The answer is: performance. Longer keys require more computation time on both the server and the client. On Fastly servers, we recently measured bit verification operations running four times faster than bit RSA key verification.
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