Key Management in Cryptography What is key management? Why are we talking about key management? Key management techniques Key management life cycle

What is key management? Definition: Key management is the set of techniques and procedures supporting the establishment and maintenance of keying relationships between authorized parties. A keying relationship is the state wherein communicating entities share common data(keying material) to facilitate cryptography techniques. This data may include public or secret keys, initialization values, and additional non-secret parameters.

What is key management (cont.)? Key management encompasses techniques and procedures supporting: 1. initialization of systems users within a domain; 2. generation, distribution, and installation of keying material; 3. controlling the use of keying material; 4. update, revocation, and destruction of keying material; and 5. storage, backup/recovery, and archival of keying material.

Why are we talking about key management? Most attacks aimed at key management level rather than cryptographic algorithm itself? Key management objectives, threats, and policy

Why are we talking about key management?  Objectives The objective of key management is to maintain keying relationships and keying material in a manner that counters relevant threats In practice an additional objective is conformance to a relevant security policy

Why are we talking about key management?  Threats 1. compromise of confidentiality of secret keys 2. compromise of authenticity of secret or public keys. 3. unauthorized use of public or secret keys

Why are we talking about key management?  Security policy Security policy explicitly or implicitly defines the threats a system is intended to address Security policy may affect the stringency of cryptographic requirements, depending on the susceptibility of the environment in questions to various types of attack.

Why are we talking about key management? Security policies also typically specify: 1. practices and procedures to followed in carrying out technical and administrative aspects of key management, both automated and manual; 2. The responsibilities and accountability of each party involved; and 3. The types of tecords to be kept, to support subsequent reports or reviews of security-related events.

Key management techniques Public-key vs. symmetric-key techniques Primary advantages offered by public-key (vs. symmetric-key) techniques for applications related to key management include: 1. simplified key management 2. on-line trusted server not required 3. enhanced functionality

Key management techniques Symmetric-key encryption plaintext ciphertext plaintext encryption decryption secret key secret key symmetric key generator

Key management techniques b) public-key encryption plaintext plaintext ciphertext encryption decryption public key private key asymmetric key pair generation secure channel (private and authentication) secure channel (authentication only) unsecured channel (no protection)

Key management techniques Techniques for distributing confidential keys - Key layering and symmetric-key certificates Key layering: 1. master keys – keys at the highest level in the hierarchy 2. key-encrypting keys – symmetric keys or encryption public keys used for key transport or storage of other keys 3. data keys – used to provide cryptographic operations on user data

Key management techniques symmetric-key certificates: Symmetric-key certificates provide a means for a KTC(Key Translation Center) to avoid the requirement of either maintaining a secure database of user secrets (or duplicating such a database for multiple servers), or retrieving such keys from a database upon translation requests.

Key management techniques Techniques for distributing public keys - Authentication trees Authentication trees provide a method for making public data available with verifiable authenticity, by using a tree structure in conjunction with a suitable hash function, and authenticating the root value. - Public-key certificates Public-key certificates are a vehicle by which public keys may be stored, distributed or forwarded over unsecured media without danger of undetectable manipulation

Key management techniques - Two public-key systems a) Identity-based system b) asymmetric system with implicitly-certified public keys

Key management techniques Techniques for controlling key usage - Key separation and constraints on key usage Information that may be associated with cryptographic keys includes both attributes which restrict their use, and other information of operational use.These include: 1. owner of key 2. validity period 3. key identifier 4. intended use 5. specific algorithm 6. system or environment of intended use, or authorized users of key 7. names of entries associated with key generation, registration, and certification 8. integrity checksum on key

Key management techniques - Key separation and threat of key misuse The principle of key separation is that keys for different purposes should be cryptographically separated. The threat of key misuse may be addressed by techniques which ensure that keys are used only for those purposes pre-authorized at the time of key creation. Techniques for controlling use of symmetric keys The main technique is the use of control vectors: Control vectors provide a method for controlling the use of keys, by combing the idea of key tags with the mechanism of simple key notarization.

Key management techniques Key management involving multiple domains - Definition A security domain is defined as a (sub)system under the control of a single authority which the entities therein trust. Trusted between two domains Two parties A and B, belonging to distinct security domains DA and DB with respectively authorities TA and TB, may wish to communicate securely. This can be reduced to the requirement that A and B either: a) Share a symmetric key b) share trusted public keys

Key management life cycle Key management is simplest when all cryptographic keys are fixed for all time. Cryptoperiods necessitate the update of keys. Key update necessitates additional procedures and protocols, often including communications with third parties in public-key systems. The sequence of states which keying material progresses through overt its lifetime is called the key management life cycle. Life cycle stages may include:

Key management life cycle 1. user registration 2. user initialization 3. key generation 4. key installation 5. key registration 6. normal use 7. key backup 8. key update 9. archival 10. key de-registration and destruction 11. key recovery 12. key revocation