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OTP Grinder

Explore OTP algorithms, build secure authentication systems, and troubleshoot with ease.

PKI SSO SAML OAuth Push notifications Zero Trust Adaptive authentication OpenID Strong authentication FIDO OCRA U2F Challenge-response PAM Risk-based authentication OTP Hard token ➠ Soft token ➠ Biometric auth OATH Passwordless Authentication factors MFA 2FA TOTP ➠ HOTP Smart card auth OpenID Connect PIN

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Public Key Infrastructure (PKI)

Public Key Infrastructure manages digital certificates, public and private keys, certificate authorities, and revocation data. PKI establishes trusted machine and user identities for TLS, document signing, device authentication, VPN access, and encrypted communication.

A secure PKI depends on protected private keys, controlled certificate enrollment, short and monitored certificate lifecycles, and reliable revocation. MFA can protect administrators and certificate-management portals, while smart cards can keep private keys in tamper-resistant hardware.

For portable symmetric token provisioning rather than certificates, see the PSKC generator.

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Single Sign-On (SSO)

Single Sign-On lets a user authenticate with an identity provider once and access multiple connected applications without entering credentials again. Enterprise SSO commonly uses SAML or OpenID Connect to exchange trusted identity information.

SSO reduces password repetition and centralizes access policy, but it also concentrates risk in the identity provider. Strong MFA, conditional access, short sessions, and rapid account deprovisioning are essential controls.

Explore practical MFA deployment options in the Protectimus authentication FAQ.

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SAML Authentication and Enterprise SSO

Security Assertion Markup Language (SAML) is an XML-based federation standard used by identity providers and service providers for browser-based enterprise SSO. A signed SAML assertion communicates the authenticated subject, attributes, audience, and validity period.

Secure deployments validate XML signatures, issuer, audience, destination, timestamps, and replay protection. Encryption can protect assertion contents, while MFA strengthens the identity-provider login.

See the OASIS SAML standard for protocol specifications.

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OAuth 2.0 Authorization

OAuth 2.0 delegates limited access to APIs without giving an application the resource owner's password. Authorization servers issue scoped access tokens to approved clients, and refresh tokens can obtain new access tokens when policy permits.

OAuth is an authorization framework, not an authentication protocol. User authentication is normally added with OpenID Connect. Modern deployments should use Authorization Code with PKCE, strict redirect URI validation, short-lived tokens, and least-privilege scopes.

Read RFC 6749 for the OAuth 2.0 framework.

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Push Notification Authentication

Push authentication sends an approval request to a registered mobile authenticator. It can provide a faster MFA experience than manually entering an OTP, especially when the request displays the service, location, device, and transaction details.

Blind approve/deny prompts can enable MFA-fatigue attacks. Number matching, transaction context, rate limits, device binding, and anomaly detection make push approvals safer.

The Protectimus Smart authenticator supports mobile authentication alongside OATH OTP algorithms.

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Zero Trust Security

Zero Trust is a security architecture that continuously verifies users, devices, workloads, and access context instead of trusting requests because they originate inside a network. Access decisions follow least privilege and assume that compromise is possible.

Typical controls include strong identity, phishing-resistant MFA, device posture, microsegmentation, just-in-time access, continuous monitoring, and rapid policy enforcement. Zero Trust is a program of coordinated controls rather than a single product.

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Privileged Access Management (PAM)

Privileged Access Management protects administrator, service, root, and other high-impact accounts. PAM platforms can vault credentials, issue temporary privileges, record sessions, rotate secrets, and require approval before sensitive access.

MFA should protect both the PAM control plane and privileged sessions. Just-in-time access, separation of duties, and searchable audit records reduce the exposure created by standing administrator privileges.

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Risk-Based and Adaptive Authentication

Risk-based authentication evaluates signals such as device reputation, IP address, location, impossible travel, behavior, and resource sensitivity. The system can allow a low-risk request, require step-up MFA, limit the session, or block access.

Effective adaptive authentication combines transparent signals with understandable fallback methods. Risk scores should support policy decisions without becoming the only security control or creating inaccessible user journeys.

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One-Time Password (OTP) Authentication

A one-time password is valid for one event or a short time window. OATH-based OTP systems derive codes from a shared secret using HOTP counters, TOTP timestamps, or OCRA challenge-response data.

OTP improves resistance to reused-password attacks, but entered codes can still be phished in real time. Protect shared secrets, validate codes over encrypted channels, limit attempts, and combine OTP with contextual controls.

Learn the algorithms in the OTP algorithms guide, then test values with the HOTP, TOTP, and OCRA tools.

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OpenID and Federated Identity

OpenID introduced decentralized web identity by allowing a user to authenticate through an identity provider instead of creating a separate password at every relying site. The original OpenID protocol is now largely replaced by OpenID Connect.

New integrations should normally use OpenID Connect, which adds a standardized authentication layer and ID tokens to OAuth 2.0.

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Strong Authentication

Strong authentication uses controls that make account takeover materially harder than password-only login. Common designs combine independent factors, protected cryptographic credentials, replay resistance, secure recovery, and risk-aware access policy.

OTP-based MFA is widely compatible, while FIDO2 and passkeys add phishing-resistant public-key authentication. The appropriate method depends on threat model, user population, recovery requirements, and regulated assurance levels.

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FIDO2 and Phishing-Resistant Authentication

FIDO authentication uses public-key cryptography so the server stores a public key rather than a reusable shared secret. FIDO2 combines WebAuthn in the browser with CTAP for external authenticators, security keys, and passkeys.

Credentials are bound to the legitimate site origin, which makes them resistant to credential phishing. Biometrics or a device PIN can unlock the local authenticator without being sent to the website.

See the W3C WebAuthn specification.

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OCRA Challenge-Response Authentication

OCRA is the OATH Challenge-Response Algorithm defined in RFC 6287. It can generate authentication or transaction-signing codes from a shared secret plus a challenge, counter, password hash, session information, or timestamp.

Because the response is tied to supplied data, OCRA can provide stronger transaction context than a standalone OTP. Both parties must use the same OCRA suite and encode every input consistently.

Build and verify suites with the OCRA generator, or consult RFC 6287.

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Universal 2nd Factor (U2F)

U2F is an earlier FIDO standard for hardware security keys used as a phishing-resistant second factor. The key creates an origin-bound public-key credential and signs a server challenge after the user confirms physical presence.

Modern applications generally implement WebAuthn and FIDO2, which expand the model to passwordless and multi-device credentials while retaining support for many existing U2F security keys.

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Challenge-Response Authentication

Challenge-response authentication proves possession of a secret or private key without sending that credential directly. The verifier supplies an unpredictable challenge, and the claimant calculates a response that the verifier can validate.

Challenges must be unique or time-limited to prevent replay. OCRA applies this model to OATH shared-secret authentication and transaction confirmation; experiment with it in the OCRA tool.

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OATH Authentication Standards

The Initiative for Open Authentication (OATH) developed interoperable specifications for one-time-password and challenge-response systems. Widely deployed algorithms include HOTP, TOTP, and OCRA.

OATH is unrelated to OAuth: OATH standardizes authentication mechanisms, while OAuth delegates API authorization. Use the local HOTP, TOTP, and OCRA generators to inspect compatible vectors.

Protectimus documents practical OATH token enrollment and management.

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Biometric Authentication

Biometric authentication verifies an inherence characteristic such as a fingerprint, face, iris, or voice. Well-designed systems keep biometric templates protected on the device and use them to unlock a cryptographic authenticator.

Biometrics are probabilistic and cannot be reissued like passwords, so enrollment, liveness detection, fallback recovery, privacy, and template protection matter. A biometric should usually unlock a device-bound credential rather than serve as a reusable remote secret.

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Passwordless Authentication

Passwordless authentication removes the memorized reusable password from the login flow. Passkeys, FIDO2 security keys, smart cards, magic links, and appropriately designed OTP systems are common approaches.

The strongest designs resist phishing, bind credentials to a device or origin, and provide controlled recovery. Organizations should evaluate enrollment and account-recovery paths as carefully as normal sign-in.

Protectimus describes an OTP-based approach in its passwordless Active Directory solution.

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Authentication Factors

Authentication factors are commonly grouped as knowledge (something you know), possession (something you have), and inherence (something you are). Location and behavior can add contextual risk signals but are not always treated as independent factors.

Using two passwords is not MFA because both are knowledge factors. Strong MFA combines independent factors and protects enrollment, device replacement, help-desk recovery, and factor reset workflows.

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Multi-Factor Authentication (MFA)

Multi-factor authentication requires evidence from at least two independent factor categories. A typical deployment combines a password with an authenticator app, hardware token, security key, smart card, or device-bound biometric credential.

MFA reduces the impact of stolen passwords, but security still depends on phishing resistance, enrollment, recovery, rate limits, and session protection. High-risk users should receive stronger methods and tighter recovery controls.

Compare supported methods in the Protectimus MFA FAQ.

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Two-Factor Authentication (2FA)

Two-factor authentication is MFA with exactly two independent factors. Common examples combine a password with a TOTP app, hardware OTP token, push approval, smart card, or FIDO security key.

2FA should protect sensitive actions as well as login, and recovery must not silently fall back to a weak single factor. Test standards-based OTP provisioning with the TOTP generator and Bulk Converter.

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HOTP: Counter-Based One-Time Passwords

HOTP generates a one-time password from an HMAC-protected shared secret and an incrementing counter. The token and server must keep their counters synchronized, and servers commonly accept a limited look-ahead window.

An unused HOTP code does not expire merely because time passes, so attempt limits and counter resynchronization policy are important. Generate test vectors with the HOTP tool or review RFC 4226.

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Smart Card Authentication

Smart cards store cryptographic keys in hardware and can authenticate users by signing a challenge. Enterprise deployments commonly combine card possession with a PIN and use PKI certificates for workstation, VPN, application, or physical access.

Security depends on certificate lifecycle management, PIN policy, card issuance, lost-card response, middleware, and trusted readers. Private keys should remain non-exportable whenever possible.

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OpenID Connect (OIDC)

OpenID Connect is an authentication layer built on OAuth 2.0. It lets a relying party verify a user's identity through an identity provider and receive standardized claims in a signed ID token.

Secure OIDC clients validate issuer, audience, signature, nonce, state, redirect URI, and token lifetime. Authorization Code with PKCE is the normal choice for modern browser and mobile applications.

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Personal Identification Number (PIN)

A PIN is a short local knowledge factor used to unlock a device, smart card, authenticator, or secure application. A device-bound PIN differs from a remote password because verification can remain inside protected hardware.

Attempt limits, lockout, secure storage, and controlled reset reduce guessing risk. A PIN should not be presented as a second factor when it protects the same remote credential and channel as the primary password.