Multi-factor Authentication Methods

Taxonomy

Abbie Barbir

Authentication Strength

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• (entity) authentication: A process used to achieve sufficient confidence in the binding between the entity and the presented identity.

• What is Authentication Strength (or Trust in the Authentication Step)?– Measures how difficult it is for imposter to masquerade as the legitimate user – Authentication strength is often more formally expressed as a "level of assurance“

(ITU X.1254 and ISO 29115 (Based on NIST 800 63))• Two-factor authentication (TFA, T-FA or 2FA) is an approach to authentication which

requires the presentation of two or more factors from the same or different category • Multi-factor authentication uses more that 2 factors from different categories• Analysis

– Overall objective is to elevate Trust in the Authentication step– Established terms, such as “2FA" are no longer precise enough to guide

technology decisions – Choosing the method or methods appropriate for the needs of securing the

enterprise using appropriate comparisons of different vendors' products and services require a more granular taxonomy

How to determine the "Best" Authentication Method

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Use Needs and Constraints to Determine• Authentication strength

• indicated by the level of risk• Total Cost of Ownership

• Constrained by budget • Ease of use

• universally desirable, but it is less critical the greater the consistency

• Other constraints • consistency and control of the

endpoint is a particular constraint;

Source of Figure is Gartner

Elevating Trust in Authentication Strength Level

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• Increasing the strength of authentication can be done by adding factors from the same or different kinds of authentication categories that don’t have the same vulnerabilities.

• There are five categories of authentication methods• who you are, • what you know, • what you have, • what you typically do and • the context.

• What you typically do consists of behavioral habits that are independent of physical biometric attributes.

• Context includes, “but is not limited” to, location, time, party, prior relationship, social relationship and source.

• Authentication assurance or elevation can be within the classic four X.1254 ITU-T LoA (ISO 29115 (NIST 800-063))

• Adding factors from different categories can increase strength only if the overall set of vulnerabilities is reduced.

Mostly used to provide

Secondary Attributes

Authentication Categories

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Who You Are

Biometric

what you

know

what you

have

what you

Do Context

Physical

Biometric

• immutable and unique• Facial recognition • Iris Scan• Retinal Scan• Fingerprint Palm Scan• Voice• Liveliness biometric

factors include:• Pulse.

CAPTCHA; etc

Behavioral

Biometric • based on person’s

physical behavioural activity patterns • Keyboard

signature• Voice

• User Name and Password (UN/PW), A passphrase, a PIN

• Very often used alone or in combinations with KBA methods.

• Knowledge Based Authentication (KBA)

• Static KBA

• Dynamic KBA

• One Time Password (OTP)

• Smart card

• X.509 and PKI

• Rarely used alone

• Used in combination with UN/PW and a PIN

• Browsing patterns

• Time of access

• Type of device

• Used in Combination with other methods

•

• Location; Time of access;

• Subscriber identity module (SIM)

• Frequency of access;

• Source and endpoint identity attributes such as

• Used in Combination of other methods

How to Evaluate Authentication Strength1. Two aspects to consider• Method's resistance to attack

– how difficult is it for an attacker to directly compromise or undermine the authentication method (without the user's knowing collusion)

• Method resistance to wilful misuse – how difficult is it for a user to deliberately allow others to share his account?

2. Authentication Strength• Measures how hard it is for another person to masquerade as the legitimate user

– Authentication may be undermined by two kinds of attacks:– Masquerade attacks, in which an attacker is (by some means) able to corroborate a falsely

claimed digital identity and, thus, log in as a legitimate user.– Session hijacking attacks, such as a man-in-the browser attack, which take control of or

parasitize an already-authenticated session after a legitimate user's claimed digital identity has been corroborated.

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Session hijacking attacks bypass authentication and, thus, can succeed no matter how strong the authentication method is. There is always a need for fraud detection, misuse monitoring and other compensating controls in order to elevate trust .

Source : Gartner

How to Evaluate Authentication Strength• Combining two or more authentication methods can potentially increases

authentication strength, compared with using either one.– For example, passwords are vulnerable to key logging– adding a second, partial password entered via drop down menu may

reduce vulnerability to this attack.• Point of Caution

– Each type of authentication attribute has a set of overlapping and intrinsic vulnerabilities with other attributes

– A combination of two attributes of the same type tends to share many of vulnerabilities

– It is a big mistake to assume that strong authentication always result when combining multiple authentication attributes/factors.

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Only by combining attributes of different kinds (that is, different factors) with different (non-overlapping) sets of vulnerabilities is there a significant increase in resistance to attack and, thus, in authentication strength

Source: OASIS, ITU, NIST, Gartner

How to Evaluate Authentication Strength• Not any MFA method is  stronger than an authentication method

based on a single authentication factor/attribute. For example,• For example, a biometric authentication method using heart

beat is stronger than a password + OTP• For some type of attacks, a 2FA method might not be stronger

than one of its components if used alone. – For example, a "fly-phishing" attack that captures and

immediately use an OTP will be equally successful whether the OTP token was PIN-protected or not.

• Some issues to consider• How Unique is the credential• Level Trust of Binding of credential to entity

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Source: NIST, Gartner

Evaluating Authentication Strength “Take Away”• Counting Factors is not enough to evaluate authentication strength

9Source: Gartner

Authentication Process Threats

• Online guessing • Phishing • Pharming

Threat Resistance per Assurance Level

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• Eavesdropping • Replay • Session hijack • Man-in-the-middle

Source: ITU-T, NIST

Example Calculating the Overall Authentication Assurance Level (LOA 3)

• The overall authentication assurance level is based on the low watermark (weakest link) of the assurance levels for each of the components of the architecture. For instance, to achieve an overall assurance level of 3:

• The registration and identity proofing process shall, at a minimum, use Level 3 processes or higher.

• The token (or combination of tokens) used shall have an assurance level of 3 or higher.

• The binding between the identity proofing and the token(s), if proofing is done separately from token issuance, shall be established at level 3.

• The authentication protocols used shall have a Level 3 assurance level or higher.

• The token and credential management processes shall use a Level 3 assurance level or higher

• Authentication assertions (if used) shall have a Level 3 assurance or higher11

Tokens• A Token is something that the Claimant possesses and controls (typically a

cryptographic module or password) that is used to authenticate the Claimant’s identity

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• Single-factor Token – • A token that uses one of the three factors to achieve authentication.

• For example, a password is something you know. • There are no additional factors required to activate the token, so

this is considered single factor.• Multi-factor Token –

• A token that uses two or more factors to achieve authentication. • For example, a private key on a smart card that is activated via PIN

is a multi-factor token. • The smart card is something you have, and something you know

(the PIN) is required to activate the token.

All Possible Token Types

1. Memorized Secret Token – A secret shared between the Subscriber and the CSP

2. Pre-registered Knowledge Token– A series of responses to a set of prompts or challenges

3. Look-up Secret Token– A physical or electronic token that stores a set of secrets shared between

the Claimant and the CSP. The token authenticator is the secret(s) identified by the prompt. Look-up secret tokens are something you have.

4. Out of Band Token – A physical token that is uniquely addressable and can receive a Verifier-

selected secret for one-time use. The device is possessed and controlled by the Claimant and supports private communication19 over a channel that is separate from the primary channel for e-authentication.

5. Single-factor (SF) One-Time Password (OTP) Device– A hardware device that supports the spontaneous generation of one-time

passwords 13

All Possible Token Types

6. Single-factor (SF) Cryptographic Device– A hardware device that performs cryptographic operations on input provided to the device.

This device does not require activation through a second factor of authentication7. Multi-factor (MF) Software Cryptographic Token

– A cryptographic key is stored on disk or some other “soft” media and requires activation through a second factor of authentication.

8. Multi-factor (MF) One-Time Password (OTP) Device – A hardware device that generates one-time passwords for use in authentication and which

requires activation through a second factor of authentication 9. Multi-factor (MF) Cryptographic Device

– A hardware device that contains a protected cryptographic key that requires activation through a second authentication factor. Authentication is accomplished by proving possession of the device and control of the key. The token authenticator is highly dependent on the specific cryptographic device and protocol, but it is generally some type of signed message. For example, in TLS, there is a “certificate verify” message. The MF Cryptographic device is something you have, and it may be activated by either something you know or something you are.

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Token Threats

15Source: NIST, ITU-T

Token Threat Mitigation Strategies

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Token Requirements Per Assurance Level

• See NIST 800-63-1

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NIST: Assurance Levels for Multi-Token E-Authentication Schemes

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Next Steps

• Identify tokens that wedo support• Determine LOA of each token• Determine LOA of each EAA cycle• Suggest a Table for LOA level• Assume No protocol for now

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Appendix 1

Token Requirements Per Assurance Level

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NIST

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NIST

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NIST

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NIST

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