Our PKI definition: A Public Key Infrastructure (PKI) provides mechanisms and services for the management of public and private keys from an asymmetric cryptosystem based on digital certificates.

PKI enables the management of cryptographic security mechanisms in large organizations. The security level may be increased significantly with PKI. Strong authentication of users, computers or services can be enforced with digital certificates. E-Mails or documents may be encrypted to any recipients using their certificates. Only PKI offers the use of digital signatures and a comprehensive trustworthy automation of business processes.

PKI offers:
- high security
- compliance
- solid basis for different security applications
- efficient identity management
- increased usability and
- cost reduction at administration and help desk

If you want to protect your internal communication, e.g. WiFi, VPN, IEE 802.1x, you can use an internal PKI with a Microsoft CA. If you want to exchange signed or encrypted e-mails or documents with external partners you are advised to use trusted certificates from a managed PKI service with a public CA. Depending on your internal cost structures it can be better to use a managed PKI also for internally used certificates. Also hybrid models can be useful.

This is done using hybrid encryption. Data will be encrypted with a session key using a performant symmetric algorithm like AES. The session key will be encrypted with the public keys from each recipient’s certificate.

You can encrypt e-mails with standard mail clients like Outlook, Notes or Thunderbird and even with mobile apps like iOS mail or some Android mail apps. You can encrypt files with your colleague’s certificates or you can encrypt a PDF using Adobe Acrobat. There are a lot of further encryption applications that you may use with digital certificates.

Your external partners need to retrieve your internal certificates from a publicly accessible certificate directory server like the Secardeo certBox. The certBox will automatically find and provide your encryption applications with external user certificates.

Seamless end-to-end encryption means that the encryption of a file or e-mail is done at your own device and that the decryption is done at the recipient’s device. Nobody on the route may intercept and read your data.

Within Windows Server, a CA software is provided under the term "Active Directory Certificate Services" (ADCS).

A Windows PKI is a series of PKI mechanisms and services around the Microsoft CA that come with the Windows operating system.

An enterprise CA is integrated with Active Directory and it supports enterprise features like certificate templates, autoenrollment and key archival. A standalone CA is primarily used for Root CA or Policy CA installations.

This can be done using a “Root Signing” service which is being offered from some public CAs. But this comes with high costs and formal efforts. An alternative is using a Certificate Enrollment Proxy like Secardeo certEP which provides the Windows clients and users automatically with globally accepted certificates from selected CAs.

Certificate templates in a Windows PKI define the content and required attributes as well as the registration workflow of certificates for specific application areas.

Windows ADCS support CRL, Delta-CRL and Online Certificate Status Protocol (OCSP).

Autoenrollment describes the automated enrollment and renewal of digital certificates. It is supported by Windows Enterprise CAs. Autoenrollement is configured using group policies. Digital certificates can be enrolled with or without user interaction.

An enrollment agent is used to request certificates on behalf of other user. The enrollment agent is primarily used for smartcard enrollment.

Key archival means the secure storage of the private encryption key. This is necessary to recover encrypted data, if the private key is lost. Key archival is configured in the certificate template and the key recovery process is performed by so called key recovery agents.

ADCS supports the Common Criteria role separation. Several user roles exist to increase the security of the CA. The following roles exist:
- CA Administrator - Manages the CA and is allowed to configure the certificate templates.
- CA Manager - Authorizes certificate requests and revokes certificates. The CA manager supports to recover private keys.
- Auditor - Analyses the security event log.
- Backup Operator - Performs the backup of the CA database, configuration and keys.

The enterprise CA publishes certificates into the active directory if this option is configured in the certificate template. User certificates are published to the corresponding user entries. Client applications like MS Outlook automatically search for these certificates to send encrypted e-mails. In order to publish certificates to the public internet, advanced certificate directory services like the Secardeo certBox are required in order to achieve a high level of security and interoperability.

A certificate trust list (CTL) is a signed list of CA certificate hash values of trustworthy CAs. A CTL is distributed using group policies and restricts the key usage for each CA.

A digital certificate (or public key certificate) is a data structure signed by a CA that contains a public key, the name of the owner of the key, the certificate lifetime and further attributes. Standard file extensions are .cer, .cert and .pem.

For the encryption of a message for a recipient, a digital certificate is required which contains the public key of the recipient. A digital certificate may also serve for the strong authentication of users, servers or hardware components. It is also used for the validation of digital signatures.

With digital certificates a huge number of applications may be protected on a very high level. The certificates of a PKI may be used for secure E-Mail, Web-Security, Windows SmartCard-Logon, VPN, File and Folder encryption as well as for digital signatures.

X.509 is an ITU-T recommendation for the structure and usage of digital certificates. X.509 certificates are supported by major operating systems and applications.

A Certificate Authority (CA) is a trusted third party that signs digital certificates or certificate revocation lists (CRLs) with its own private key.

A certificate revocation list (CRL) contains the serial numbers of certificates that have been revoked and therefore must not be used any more. It can contain further information as the time of revocation and the revocation reason code.

A certificate chain contains all certificate from a user or computer (end entity certificate) via the issuing CA and intermediate CAs (intermediate CA certificate) up to a trusted root CA (root CA certificate).

PKCS#12 is a standard of RSA Labs that specifies a portable format for storing or transporting a user's private keys, certificates etc. A PKCS#12 container can be encrypted using a password. Standard file extensions are .p12 and .pfx.

A PKI token is a crypto hardware component usually in the form factor of a USB dongle. Typically, this USB dongle contains a smart card chip where the crypto operations are performed and private keys and certificates are stored. So, it combines security and usability, as no additional smart card reader is needed. While this is a feasible tool for Windows computers, support for mobile devices is mostly not available.

A Hardware Security Module (HSM) is a hardware component to generate and store private keys of a CA or other PKI services. Additionally, a HSM performs cryptographic operations. One can differentiate between dedicated and network HSMs. Dedicated HSMs are directly connected to one CA, whereas network HSMs can be used by multiple CAs.

Digital signatures are data structures which are created through a cryptographic calculation of a document or an e-mail with the private key of the signer. Everyone may validate the integrity and authenticity of the digitally signed document using the signer's public key. Furthermore one can prove unambiguously who has signed the document.

Digital signatures based on asymmetric cryptography provides the following advantages:
- Saving of time
- Cost reduction
- Increased Security
- Compliance
- Legal binding

Faking e-mails is very popular in order to inject malware or to place a malicious business instruction, e.g. “Please transfer ### dollars to account XYZ immediately, Sincerely your CEO”. This can be avoided by signing e-mails that prove the real originator and the message integrity with no doubt. For internal processes you can use certificates from your inhouse CA, e.g. a Microsoft CA. For external communication you should use trusted S/MIME certificates from a public CA.

The most common digital signature format is PKCS#7. It is used in PDF, S/MIME and so called detached signatures. A different popular format is PGP, which may be used for files and e-mails. XML-DSig offers an XML based format for digital signatures. It is used in Microsoft Office and OpenOffice.

The Portable Document Format (PDF) allows to digitally sign a document by inserting a cryptographic signature value in the file. When viewing the document, such a signature is typically represented by a signature field containing the name and further attributes of the signer. By using PDF signatures, later modifications of a document will be indicated by the PDF Viewer.

The signature legislation defines basic, advanced and qualified signatures. The requirements are set forth under EU Regulation No 910/2014 (eIDAS-regulation). An advanced electronic signature can be implemented using an asymmetric cryptosystem. A qualified electronic signature is an advanced electronic signature that has been generated by using a qualified certificate. A qualified signature is legally binding like a handwritten signature.