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1-2-2 Authentication Technique

(1) User authentication

User authentication is an authentication technique that includes the process of verifying a user’s identity. It is used as a measure against the impersonation of authorized users by malicious third parties. In user authentication, there are a variety of methods according to purpose and application.

(1) User ID/Password A user ID is an identifier that is assigned to an individual user, while a password is a character string (i.e., a keyword) that is registered in advance. During the login process, this technique searches for a registered password corresponding the user ID entered by the user. If the registered password matches the password entered by the user, the user is authenticated as a valid user who knows the password. When this technique is used, it is necessary for users to thoroughly follow password management and password requirements to prevent any abuse of passwords.

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(2) IC card This is a technique that authenticates users through plastic IC cards with embedded IC chips that are able to record information. It is used for commuter passes, employee ID cards, etc. When an IC card is used, the user may be asked to enter the PIN code (Personal Identification Number) recorded in the IC chip in order to confirm that the user is the rightful holder of the card. IC cards have over 100 times more storage capacity than magnetic cards and enable data encryption to make the cards resistant to forgery. The cards also have an advantage in tamper resistance to prevent unauthorized access or falsification.

(3) OTP (One-Time Password) This is a password-based user authentication technique that is primarily used by computers connected to communication lines. By using a different password for each login, this technique avoids the risk of password leakage. Typical one-time password methods are as follows:

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(4) Biometric authentication This authentication technique identifies an individual (i.e., a user) by using physical information or behavioral information (e.g., speed or pen pressure used in a signature) that is unique to the individual, and such information is registered in advance on the authentication system. In addition to managing entry into secure areas, this authentication is also used by bank ATMs and individual PCs. Although it is effective in preventing spoofing, it requires special authentication systems and continues to present issues in areas such as authentication precision (FRR (False Rejection Rate) and FAR (False Acceptance Rate)), difficulty of substitution, adaptation to physical changes over time, and personal information protection. · 1 question

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(5) Public key cryptography This is an authentication technique that uses private keys that are kept secret by the holders.

Step (3) is the key point in user authentication. The fact that Recipient B successfully performed decryption using Sender A’s public key means that the cipher text had been encrypted using A’s private key (because cipher text encrypted from plain text by using one of the key pairs can only be decrypted using the other key). Since only A has (i.e., conceals) A’s private key, this cipher text cannot be created by any party other than A. In other words, it is confirmed (i.e., authenticated) that the sender is unquestionably A. However, it is necessary to note that this authentication works well on the assumption that A’s public key, which B has, must belong to A without doubt, and its paired private key must be owned by A alone.

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(2) Message authentication

Message authentication is an authentication technique that confirms that data is not improperly overwritten. It is used as a measure to prevent falsification involving improper overwriting of data. As a typical message authentication method used in data communication, there is a method of calculating a message digest from the communication text (i.e., the data) by using a hash function. · 3 questions

On the basis of the property of a hash function, if there is even a small difference in the communication text between the sender side and the recipient side, the message digests that

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are delivered to and generated by the recipient side will be different, and as a result, falsification can be detected. However, when an already-known hash function is used, there is a possibility that both the communication text and the message digest can be falsified so as not to be detected. MAC (Message Authentication Code) is a technique that can resolve this issue. This method uses a key (i.e., a common key) owned by the sender and the recipient, and also uses a MAC value, which is calculated from the communication text plus the common key, as a message digest. (As a method for calculating the MAC value, a block cipher mode of operation or a hash function is used.) When this method is used, a third party who does not know the common key cannot calculate the correct MAC value, and therefore, the level of security is enhanced.

(3) Digital signature

Digital signature is an authentication technique that combines user authentication and message authentication using public key cryptography. (To distinguish digital or other electronic-based signatures from regular signatures, these are sometimes called electronic signatures.) · 2 questions

A typical digital signature method is DSA (Digital Signature Algorithm) developed by NIST

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(National Institute of Standards and Technology) as a US government standard. DSA is an improved version of ElGamal signature, which uses the ElGamal encryption scheme known as one of the public key cryptography standards, and generates message digests using SHA-1 or SHA-2. It is noted that SHA-1 is being migrated to SHA-2 (e.g., a general term for SHA-256, SHA-512). Another method is the W3C-recommended XML signature, which defines a digital signature syntax for XML documents. XML signatures can be attached to communication text like normal signatures, and can also be attached to specified elements or content. In digital signatures, third parties (private companies) known as certification bodies guarantee the validity of public and private keys on which user authentication by public key cryptography is predicated. These certification bodies are also used for specified purposes (e.g., public key cryptography) other than digital signatures.

Certification bodies are composed of third-party organizations, such as CA (Certification Authority), RA (Registration Authority), and VA (Validation Authority), which issue digital certificates to users and lower-level certification authorities in order to guarantee the validity of public keys and digital signatures. In addition, in order to certify the validity of certification bodies themselves and distribute public keys, they issue root certificates signed with their own private keys. · 1 question

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CAs (Certification Authorities) include two types of CAs: public CA that issues certificates for external web services, and private CA that takes on a role within a closed environment, such as a specified organization.

(4) Other certification techniques

(1) Time authentication (timestamp authentication) This is a certification technique by which a third-party time stamping authority (TS authority, which may be a certification authority) guarantees the existence and authenticity of electronic documents, in accordance with the Japanese Act on Utilization of Telecommunications Technology in Document Preservation, etc. Conducted by Private Business Operators, etc. of 2005. Normally, a creator’s digital signature and digital certificate are attached to an electronic document. · 1 question

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(2) IEEE 802.1X This is a client authentication technique used for LANs. It is implemented using a RADIUS server or other authentication server, and authentication software (i.e., supplicant).

(3) CAPTCHA (image authentication) This is an authentication technique that requires users to identify a distorted image of letters or numbers displayed on the screen and then enter the corresponding correct characters, in order to confirm that they are human beings. It is used to prevent automatic posting by programs and such other automated processes.