The way to verify the SSL private key length of any website!

The way to verify the SSL private key length of any website!

Users are increasingly concerned about the security of the website they visit. Attempts at ID theft, stealing information and spoofing websites are now common occurrences.  To combat these threats, websites now use the RSA standard protocols to verify the authenticity of websites and encrypt traffic between the browser and the website.

The most common implementation for websites is SSL/TLScertification and using SSL protocols is fast becoming the de facto standard in website design.   Most browsers and websites now use the https:// prefix, stating that the site has an SSL/TLS certificate and requires an SSL connection.

Creating a domain needs registration, and creating a website needs certification. Both are relatively easy tasks, usually carried out by a Managed Service provider like HostSailor.

SSL Signs for the security
SSL private key length


Take a closer look at the PKCS, RSA and SSL/TLS!


  • The IT industry uses a standard for the structure and operation of public and private keys called PKCS.
  • PKCS was created in the early 1990s and developed as a set of vendor-independent common standards for secure information exchange. PKCS is a set of fifteen standards that define how applications should interact in certain situations.
  • The RSA standards are an inherent part of PKCS and are used in SSL/TLS.



What is an RSA Private Key?

3 things refer to the the SSL private key "website security"
RSA Private Key


RSA defines a key pair that authenticates a website’s identity and encrypts information travelling between a browser and the website.   The public key is freely available and is used to encrypt data as it travels.  The other key, the private key, is used to decrypt data and should be kept as securely as possible.

SSL/TLS follows this standard.  As the browser connects, it verifies the website‘s identity from certificate information held in the private key and establishes an encrypted session between the browser and the site using the key information.  A validation failure means no connection.




How long is an SSL Key?


SSL encryption used to be based around a key size of 1024 bits, but ever since they were cracked, are not now used for websites or PGP.  Most browsers and websites now use 2048 bit keys, but 4096 bits are becoming more popular.  Whether to use 2048 bit or 4096 bit is a common topic of discussion currently.  Debian recommends 4096 bits. However, some applications, particularly smart cards, only support 2048 bit keys.


What is the length of a private key?


Depending on the implementation, a private key is usually 2048 or 4096 bits long. It is important to remember that the key length is specified in bits, but most measurements are in bytes.  The keys also have an internal structure which can vary from implementation to implementation, so you are sometimes not comparing apples with apples.  A website SSL private key also contained information about the website and its SSL certification that allows its authenticity to be verified.

See here for a description of the structure of the private key.


Are Private Keys And Public Keys The Same Length?


Not necessarily. Keys are made from the same basic number, the modulus, and an exponent. A public exponent for the public key, and a private one for the private key. Depending on the exponents, the keys can be the same or have different lengths.



How to get your Public Key length?

How you do it varies depending on the browser, but the basic principle is the same.  You need to look at the website’s certificate details. The details will show who issued the site certificate and other information, and for our purposes here, the public key length.  Private key lengths are not disclosed.


Which SSL Key is Most Secure?



It takes about 100 hours of computing time to crack a 1024 SSL private key. Doubling the size to 2048 bits doesn’t mean it can be cracked in 200 hours, the actual time is measured in centuries. Doubling again to 4096 bits makes it impossible to crack using current technologies.  However, it is alleged that quantum computing and the faster hardware platforms can crack a 4096 bit key in under six months.

Therefore, a 2048 bit private SSL key gives all but the most security-conscious user a high degree of security. 4096 bit private keys are the most secure.


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