Chapter 5 Key Management, Exchange and Distribution PDF

Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Course Cryptography (Classic & Modern) CHAPTER 5 : Key Management, Exchange and Distrib...

Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Course Cryptography (Classic & Modern) CHAPTER 5 : Key Management, Exchange and Distribution Dr. Ahmed AlMokhtar Ben Hmida College of Computer Science, King Khaled University 'KKU', KSA Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA CHAPTER 5 : Key generation, Management, Exchange and distribution ❑Public key Distribution ❑ Public key Certificate ❑ Certificate X.509 Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Public key distribution in cryptography? Method of cryptography that requires two separate keys: One Private for decrypting the data and one public for encrypting the data in order to protect it from unauthorized access or use. Anyone can obtain the public key; it makes no difference who has and knows it. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA What is meant by key distribution? Transport of a key and other keying material from an entity that either owns or generates the key to another entity that is intended to use the key. How are public and private keys distributed? The sender obtains a copy of the recipient's public key, either by email or from a key chain server, and uses it to encrypt the message. The resulting ciphertext is then sent to the recipient who uses their corresponding private key to restore the original plaintext. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Public Announcement of Public Keys There is some broadly accepted public-key algorithm, such as RSA: any participant can send his or her public key to any other participant or broadcast the key to the community at large This approach is convenient, it has a major weakness: Anyone can forge such a public announcement. That is, some user could pretend to be user Aand send a public key to another participant or broadcast such a public key. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Key Distribution In Public Key Cryptography, the Key Distribution of public keys is done through public key servers. When a person creates a key-pair, they keep one key private and the other, known as the Public-Key, is uploaded to a server where it can be accessed by anyone to send the user a private, encrypted, message. Who can Public Keys be distributed to? Anyone ; as for Public key encryption One key is nominated as the Private Key and is kept secret. The other key is distributed to anyone who wants it for encrypting… the Public Key. Anyone can encrypt by using Public Key, but only you can read it with your Private Key... Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Key Management Security of any cryptosystem depends upon how securely its keys are managed. Without secure procedures for the handling of cryptographic keys, the benefits of the use of strong cryptographic schemes are potentially lost. It is observed that cryptographic schemes are rarely compromised through weaknesses in their design. However, they are often compromised through poor key management. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Key Management: Important aspects of key management, as follows − Cryptographic keys are nothing but special pieces of data. Key management refers to the secure administration of cryptographic keys. Key management deals with entire key lifecycle as depicted in the following illustration − There are two specific requirements of key management for public key cryptography. o Secrecy of private keys. Throughout the key lifecycle, secret keys must remain secret from all parties except those who are owner and are authorized to use them. o Assurance of public keys: are in open domain and seen as public pieces of data. By default there are no assurances of whether a public key is correct, with whom it can be associated, or what it can be used for. Thus key management of public keys needs to focus much more explicitly on assurance of purpose of public keys. Most crucial requirement of ‘assurance of public key’ can be achieved through Public-key infrastructure (PKI), a key management systems for supporting public-key cryptography. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Public Announcement of Public Keys Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Publicly Available Directory A greater degree of security can be achieved by maintaining a publicly available dynamic directory of public keys. Maintenance and distribution of the public directory would have to be the responsibility of some trusted entity or organization Publicly Available Directory: In this type, the public key is stored in a public directory. Directories are trusted here, with properties like Participant Registration, access and allow to modify values at any time, contains entries like {name, public-key} Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Publicly Available Directory 1. The authority maintains a directory with a {name, public key} entry for each participant. 2. Each participant registers a public key with the directory authority. Registration would have to be in person or by some form of secure authenticated communication. 3. A participant may replace the existing key with a new one at any time, either because of the desire to replace a public key that has already been used for a large amount of data, or because the corresponding private key has been compromised in some way. 4. Participants could also access the directory electronically. For this purpose, secure, authenticated communication from the authority to the participant is mandatory. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Public-Key Authority Stronger security for Public-Key Distribution can be achieved by providing tighter control over the distribution of public keys from the directory. The scenario in next slide assumes that a central authority maintains a dynamic directory of public keys of all participants. In addition, each participant reliably knows a public key for the authority, with only the authority knowing the corresponding private key. Publicly Available Directory: A greater degree of security can be achieved by maintaining a publicly available dynamic directory of public keys. Maintenance and distribution of the Public directory would have to be the responsibility of some trusted entity or organization (Figure 14.10).Such a scheme would include the following elements: Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Public-Key Authority Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Public-Key Authority Stronger security for public-key distribution can be achieved by providing tighter control over the distribution of public keys from the directory (A typical scenario is illustrated in Figure 14.11). Scenario assumes that a central authority maintains a dynamic directory of public keys of all participants. In addition, each participant reliably knows a public key for the authority, with only the authority knowing the corresponding private key. The following steps occur. 1. A sends a timestamped message to the public-key authority containing a request for the current public key of B. 2. The authority responds with a message that is encrypted using the authority’s private key, PRauth. Thus, A is able to decrypt the message using the authority’s public key. Therefore, A is assured that the message originated with the authority. The message includes the following: B’s public key, PUb, which A can use to encrypt messages destined for B The original request used to enable A to match this response with the corresponding earlier request and to verify that the original request was not altered before reception by the authority Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA CHAPTER 5 : Key generation, Management, Exchange and distribution ❑Public key Distribution ❑ Public key Certificate… ❑ Certificate X.509 Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Digital Certificate Considered as the ID card issued to the person (Passport, Driver's license, identity….), Digital Certificates are not only issued to people but they can be issued to computers, software packages or anything else that need to prove the identity in the electronic world. Digital certificates are based on the ITU standard X.509 which defines a standard certificate format for public key certificates and certification validation. Hence digital certificates are sometimes also referred to as X.509 certificates. Public key pertaining to the user client is stored in digital certificates by Certification Authority (CA) along with other relevant information such as client information, expiration date, usage, issuer etc. CA digitally signs this entire information and includes digital signature in the certificate. Anyone who needs the assurance about the public key and associated information of client, he carries out the signature validation process using CA’s public key. Successful validation assures that the public key given in the certificate belongs to the person whose details are given in the certificate. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Process of obtaining Digital Certificate by a person/entity Certifying Authority (CA) CA issues certificate to a client and assist other users to verify the certificate. CA takes responsibility for identifying correctly the identity of the client asking for a certificate to be issued, and ensures that the information contained within the certificate is correct and digitally signs it. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Key Functions of CA ❑ Generating key pairs: CA generate a key pair independently or jointly with the client. ❑ Issuing digital certificates − The CA could be thought of as the PKI equivalent of a passport agency − the CA issues a certificate after client provides the credentials to confirm his identity. The CA then signs the certificate to prevent modification of the details contained in the certificate. ❑ Publishing Certificates − The CA need to publish certificates so that users can find them. There are two ways of achieving this. One is to publish certificates in the equivalent of an electronic telephone directory. The other is to send your certificate out to those people you think might need it by one means or another. ❑ Verifying Certificates − The CA makes its public key available in environment to assist verification of his signature on clients’ digital certificate. ❑ Revocation of Certificates − At times, CA revokes the certificate issued due to some reason such as compromise of private key by user or loss of trust in the client. After revocation, CA maintains the list of all revoked certificate that is available to the environment. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Classes of Certificates : four typical classes of certificate − ❑ Class 1 − These certificates can be easily acquired by supplying an email address. ❑ Class 2 − These certificates require additional personal information to be supplied. ❑ Class 3 − These certificates can only be purchased after checks have been made about the requestor’s identity. ❑ Class 4 − They may be used by governments and financial organizations needing very high levels of trust. Registration Authority (RA) CA may use a third-party Registration Authority (RA) to perform the necessary checks on the person or company requesting the certificate to confirm their identity. The RA may appear to the client as a CA, but they do not actually sign the certificate that is issued. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Public-Key Certificates The scenario of Figure 14.12 is attractive, yet it has some drawbacks. The public- key authority could be somewhat of a bottleneck in the system, for a user must appeal to the authority for a public key for every other user that it wishes to contact. An alternative approach is to use certificates that can be used by participants to exchange keys without contacting a public-key authority, in a way that is as reliable as if the keys were obtained directly from a public-key authority. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Public-Key Certificates Requirements on this scheme: 1, Any participant can read a certificate to determine the name and public key of the certificate’s owner. 2, Any participant can verify that the certificate originated from the certificate authority and is not counterfeit. 3, Only the certificate authority can create and update certificates. 4, Any participant can verify the time validity of the certificate. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Public-Key Certificates Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Which is the most secure public key distribution? Public certificates are the most secure key distribution/management systems right now. Which systems use a timestamp? Public announcements and Public Certificates involve the use of timestamps. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Public Key Infrastructure (PKI) According to the X.509 standard : Publish / CA Directory Publish the revocation Request / Issue Public Key Infrastructure (PKI) is a set of roles, policies, hardware, software and procedures needed to create, manage, distribute, use, store and revoke digital certificates Final user and manage public-key encryption. But : The CA must verify the details of each user CA Security Risks Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Publish / What is a PKI and how does it CA Directory Publish the work? revocation Request / Issue Public key infrastructure (PKI) refers to tools used to create and manage public keys for RA encryption, which is a common method of securing data transfers on the End users internet. Registration Authority (RA) PKI is built into all web browsers Intermediate between key holder and CA used today, and it helps secure Verifies user requests and forwards them to the CA public internet traffic. The level of verification depends on the certification policy (CPS) implemented Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Main – CA Certificate Authority – RA Registration Authority – Publishing Directory – Administrators Complementary – Database – Timestamp server. – HTTP, SMTP, POP server. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Certificate Management System (CMS) CMS through which certificates are published, temporarily or permanently suspended, renewed, or revoked. Certificate management systems do not normally delete certificates because it may be necessary to prove their status at a point in time, perhaps for legal reasons. A CA along with associated RA runs certificate management systems to be able to track their responsibilities and liabilities. Private Key Tokens Public key of a client is stored on the certificate, the associated secret private key can be stored on the key owner’s computer (not adopted in general). Private key is stored on secure removable storage token access to which is protected through a password. Different vendors often use different and sometimes proprietary storage formats for storing keys. For example, Entrust uses the proprietary.epf format, while Verisign, GlobalSign, and Baltimore use the standard.p12 format. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Hierarchy of CA With vast networks and requirements of global communications, it is practically not feasible to have only one trusted CA from whom all users obtain their certificates. Secondly, availability of only one CA may lead to difficulties if CA is compromised. In such case, the hierarchical certification model is of interest since it allows public key certificates to be used in environments where two communicating parties do not have trust relationships with the same CA. ❑ The root CA is at the top of the CA hierarchy and the root CA's certificate is a self-signed certificate. ❑ The CAs, which are directly subordinate to the root CA (For example, CA1 and CA2) have CA certificates that are signed by the root CA. ❑ The CAs under the subordinate CAs in the hierarchy (For example, CA5 and CA6) have their CA certificates signed by the higher-level subordinate CAs. Certificate authority (CA) hierarchies are reflected in certificate chains. A certificate chain traces a path of certificates from a branch in the hierarchy to the root of the hierarchy. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA The following illustration shows a CA hierarchy with a certificate chain leading from an entity certificate through two subordinate CA certificates (CA6 and CA3) to the CA certificate for the root CA. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Verifying a certificate chain is the process of ensuring that a specific certificate chain is valid, correctly signed, and trustworthy. The following procedure verifies a certificate chain, beginning with Certificate that is presented for authentication − ❑ A client whose authenticity is being verified supplies his certificate, generally along with the chain of certificates up to Root CA. ❑ Verifier takes the certificate and validates by using public key of issuer. The issuer’s public key is found in the issuer’s certificate which is in the chain next to client’s certificate. ❑ Now if the higher CA who has signed the issuer’s certificate, is trusted by the verifier, verification is successful and stops here. The issuer's certificate is verified in a similar manner as done for client in above steps. This process continues till either trusted CA is found in between or else it continues till Root CA. Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA CHAPTER 5 : Key generation, Management, Exchange and distribution ❑Public key Distribution ❑ Public key Certificate… ❑ Certificate X.509 Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Trust model in X.509 Hierarchical infrastructure Possibility of certification between 2 CAs belonging to different trees, this is co-certification CA1 CA2 1 CA1 co-certifies CA2 1 2 3 2 3 5 5 4 1 CA Final user 12/03/2023 Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA X.509 certificates Main format used for certificates Standard: ITU-T X.509, or ISO/IEC 9594-8 Successive versions: 1988: v1 1993: v2 = v1 + 2 new fields 1996: v3 = v2 + extensions Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Structure Release (V1) Serial Number (V1) CA private key X.509 certificate Signature Algorithm Identifier (V1) (for the signature of the certificate issuer) Issuer (V1) (CA Name X500) Validity (V1) Signature (Start and end dates of the certificate) generation Subject (V1) (X500 name of holder) SubjectPublicKeyInformation (V1) (Algorithm identifier and public key) IssuerUniqueIdentifier (V2) SubjectUniqueIdentifier (V2) Extensions (V3) CA digital signature Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Structure an X.509 certificate – IssuerUniqueIdentifies uniquely identifies the key used by the CA to sign the certificate (case where the CA has used several keys since its implementation) – SubjectUniqueIdentifier Differentiates between several public keys, issued by the same CA, belonging to the same holder Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Structure X.509 certificate Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA X.509 Certificate Extensions The original concept of X.509 certificates is to bind the identity of an entity to a public key New situations: need to have information other than identity Solution: Introduction of data blocks that can support any type of information to meet local needs Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA X.509 Certificate Extensions (following) Addition of new fields without modifying the ASN.1 definition of a certificate Allow the addition of extensions according to the needs of the implementations The identifier of an extension is defined according to ITU-T Rec. X.660 | ISO/IEC 9834-1 Identifier Extension1 Critical flag (1 or 0) Extension1 Value Extension2 Identifier Critical flag (1 or 0) Extension2 Value Extension3 Identifier Critical flag (1 or 0) Extension3 value Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA X.509 Certificate Extensions (continued) The extensions are classified into 4 categories: Key and policy information extensions Holder and issuer information extensions Extensions of constraints on the certification path Revocation Extensions Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Key Usage : defines the use of the certified key digitalSignature non-repudiation keyEncipherment keyAgreement keyCertSign / cRLSign Extended Key Usage : other use cases ServerAuthentication clientAuthentication codesigning emailProtection timeStamping Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Security Key and Policy Information Extensions (continued) Private Key usage Period: defines the start and end dates of validity of the private key A signature can be valid for 10-20 years, but the private key should only be used for 1 or 2 years Certificate Policies CA policy information under which the certificate was issued X.509 delegates to the policy of the CA everything concerning the trust semantics of the certificate Several policies are used to protect the CA from liability « Verisign disclaimers any warranties … Varisign makes no representation that any CA or user to which it has issued a digital ID is in fact the person or the organization it claims to be … Verisign makes no assurances of the accuracy , authenticity , integrity , or reliability of information ” Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Information Extensions on the subject and the issuer Alternate Name ( Subject / Issuer ) or General Name rfc822 name (email address) name (DNS name of a machine) uniformResourceIdentifier (URL) IP adress X.400 address EDI (Electronic Data Interchange) name OID Any other form of noun... Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Information Extensions on the subject and the issuer (continued) Subject directory attributes Carries a sequence of attributes regarding the subject of the certificate: a role, a group membership, an authorization, a telephone number… Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Extensions of constraints on the certification path Basic Constraints Specifies whether the issued certificate is a CA certificate or not If the certificate issued is a CA certificate, a "Certification distance" is defined Name Constraints used in CA certificates indicates a namespace where all subsequent subject names in the certification path should occur Policy Constraints Explicit identification of the security policy Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University Cryptography (Classic & Modern) College of Computer Science ; King Khalid University ; KKU - KSA Revocation Extensions CRL Distribution Points identifies CRL distribution points Freshest CRL identifies the CRL that has the most recent information Ahmed AlMokhtar BEN HMIDA, Dr. & Full Professor, Head of ATMS Lab, Expert in Signal Processing , CS College at King Khalid University