Digital Certificate (SSL) Overview

Digital Certificate

The digital equivalent of an ID card used in conjunction with a public key encryption system. Also called "digital IDs," digital certificates are issued by a trusted third party known as a "certification authority" (CA) such as VeriSign ( and Thawte ( The CA verifies that a public key belongs to a specific company or individual (the "subject"), and the validation process it goes through to determine if the subject is who it claims to be depends on the level of certification and the CA itself.

Creating the Certificate

After the validation process is completed, the CA creates an X.509 certificate that contains CA and subject information, including the subject's public key (details below). The CA signs the certificate by creating a digest (a hash) of all the fields in the certificate and encrypting the hash value with its private key. The encrypted digest is called a "digital signature," and when placed into the X.509 certificate, the certificate is said to be "signed."

The CA keeps its private key very secure, because if ever discovered, false certificates could be created.

Verifying the Certificate

The process of verifying the "signed certificate" is done by the recipient's software, which is typically the Web browser. The browser maintains an internal list of popular CAs and their public keys and uses the appropriate public key to decrypt the signature back into the digest. It then recomputes its own digest from the plain text in the certificate and compares the two. If both digests match, the integrity of the certificate is verified (it was not tampered with), and the public key in the certificate is assumed to be the valid public key of the subject.


At this point, the subject's identity and the certificate's integrity (no tampering) have been verified. The certificate is typically combined with a signed message or signed executable file, and the public key is used to verify the signatures. The subject's public key may also be used to provide a secure key exchange in order to have an encrypted two-way communications session (also see articles / info on PKI and SSL)

Alentus has made 1-Year, 2-Year and 3-Year SSL Certificates to its clients through our sister company These are available for purchase through the profile. Once logged in, select "Order SSL Certificate" from the left-hand menu, and select the SSL Certificate of your choice.

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