The Tectia client-side components authenticate the Secure Shell server in order to verify that they are connecting to the correct server. Likewise, the Secure Shell server authenticates the client user. The server can be authenticated by either (plain) public-key authentication or certificate authentication. When certificate authentication is used, the public key is included in the certificate that the server sends to the client.

In (plain) public-key authentication, the server sends its public key to the client at the beginning of the first connection, and after the user has once verified and accepted the key, it is used in all future connections to that server.

In certificate authentication, the Tectia client-side components rely on a trusted third party, a certification authority (CA) to verify the server's identity. The signature of the certification authority in the server certificate guarantees the authenticity of the server certificate.

Client-side users can use certificates as proof of their identity. Certificates work like passports; the user proves his or her identity to a certificate authority once using public keys, receives a certificate, and from then on can authenticate using the certificate.

Public-key authentication (without certificates) provides an easy-to-deploy and secure means of authenticating the users without the need to deploy and maintain a public-key infrastructure (PKI). Users will create key pairs for themselves and upload the public keys to the server for verification.

Tectia Client and ConnectSecure incorporate authentication agent functionality that allows the caching of passphrases, eliminating the need to retype the passphrase each time when a connection is made. Passphrases are used in public-key authentication, which is more secure than password authentication. In addition, authentication can be "forwarded" to another host, allowing administrators to hop from one server to another without the need to store private keys in multiple servers.

Tectia supports secure password-based authentication. Unlike in plaintext protocols such as Telnet and FTP, passwords are never sent in plaintext format over the network, thus eliminating the risk of password exposure to unauthorized parties.

Tectia supports X.509 v3 certificates for further security and scalability in large and dynamic network environments. Comprehensive support for IETF PKIX and PKCS standards ensures seamless interoperability with third-party PKI products.

Tectia supports both Certificate Revocation Lists (CRLs) and Online Certificate Status Protocol (OCSP) for centralized revocation of user credentials. CRLs are automatically fetched from a local file or by using HTTP or LDAP, depending on the local settings and the CRL Distribution Point extension in the certificate. CRLs can also be imported offline in legacy environments.

Tectia supports IETF PKIX standards (CMPv2) and Cisco Systems' Simple Certificate Enrollment Protocol (SCEP) for online certificate enrollment. Certificates can also be imported by using the PKCS#12 envelope format supported by most Certification Authorities (CAs).

Tectia Client and ConnectSecure support smart cards, USB tokens, and other PKI authentication devices by supporting PKCS#11 and MSCAPI for interfacing with authentication keys. Strong, two-factor authentication overcomes the inherent security issues of password authentication.

Host-based authentication is a form of delegated trust authentication, where the Secure Shell server trusts the Secure Shell client host to authenticate the user. The user is verified by a suid binary (ssh-signer) on the client host which then confirms the user identity to the server in a communication signed with a root-owned host key. The client host is authenticated strongly with public key cryptography, thus the authentication does not rely solely on a host IP address or domain name. The Secure Shell host-based authentication utilizes strong cryptography for host identity verification.

Keyboard-interactive is a standards-based method of integrating Secure Shell with third-party authentication mechanisms that are based on keyboard input, without the need to modify the client-side application (Tectia Client). Keyboard-interactive is commonly used in conjunction with PAM and RADIUS on the server side.

Tectia Server for IBM z/OS supports the legacy OpenSSH public-key format used by IBM Ported Tools, eliminating the need for manual key conversions in multi-vendor Secure Shell environments. The key-compatibility feature also allows easy migration of OpenSSH and IBM Ported Tools environments to Tectia.