Practices in Security Practices in Security

Bruhadeshwar BezawadaBruhadeshwar Bezawada

Key ManagementKey Management

Set of techniques and procedures supporting Set of techniques and procedures supporting the establishment and maintenance of keying the establishment and maintenance of keying relationships between authorized partiesrelationships between authorized parties Initialization of system users within a domainInitialization of system users within a domain Generation, distribution, and installation of keying Generation, distribution, and installation of keying

materialmaterial Controlling the use of keying materialControlling the use of keying material Update, revocation and destruction of keying Update, revocation and destruction of keying

materialmaterial Storage, backup/recovery, and archival of keying Storage, backup/recovery, and archival of keying

materialmaterial

Types Key ManagementTypes Key Management

Automated Key ManagementAutomated Key Management More than N^2 KeysMore than N^2 Keys Stream cipherStream cipher Initialization vectors are usedInitialization vectors are used Large amount of data needs to be encrypted in short Large amount of data needs to be encrypted in short

amount of timeamount of time Long term session keys are used in multicast sessionsLong term session keys are used in multicast sessions Frequent change in session key is expectedFrequent change in session key is expected

Manual key managementManual key management Environment has limited bandwidth or high RTTEnvironment has limited bandwidth or high RTT Information has low valueInformation has low value Total volume of traffic is very lowTotal volume of traffic is very low Scale of each deployment is very limitedScale of each deployment is very limited

Cryptographic PrimitivesCryptographic Primitives

Hash FunctionsHash Functions Symmetric key algorithmsSymmetric key algorithms Asymmetric key algorithmsAsymmetric key algorithms

Cryptographic primitivesCryptographic primitives

Hash functions do not require keys, Hash functions do not require keys, provideprovide data authentication and integrity servicesdata authentication and integrity services compression of messages for digital compression of messages for digital

signature and verificationsignature and verification derivation of keys in key establishment derivation of keys in key establishment

algorithmsalgorithms generate deterministic random numbersgenerate deterministic random numbers

Cryptographic primitivesCryptographic primitives

Symmetric key algorithms require the Symmetric key algorithms require the same key across all operations, same key across all operations, provide provide data confidentialitydata confidentiality authentication and integrity in the form of authentication and integrity in the form of

MACsMACs key establishmentkey establishment generation of deterministic random generation of deterministic random

numbersnumbers

Cryptographic primitivesCryptographic primitives

Asymmetric key, public key algorithms, Asymmetric key, public key algorithms, enableenable digital signaturesdigital signatures establish cryptographic keying materialestablish cryptographic keying material generate random numbersgenerate random numbers

Exercise : Enumerate all hash functions, all Exercise : Enumerate all hash functions, all symmetric key ciphers and all public-key symmetric key ciphers and all public-key crypto systems available currently. crypto systems available currently. Differentiate between commercially available Differentiate between commercially available and non-commercial algorithmsand non-commercial algorithms

Types of keysTypes of keys

Private signature key (public-private Private signature key (public-private keys)keys)

Public signature verification keysPublic signature verification keys Symmetric authentication keySymmetric authentication key Private authentication keyPrivate authentication key Public authentication keysPublic authentication keys Symmetric data encryption keySymmetric data encryption key

TypesTypes

Symmetric and asymmetric random Symmetric and asymmetric random number generation keysnumber generation keys

Symmetric master keySymmetric master key Private key transport keyPrivate key transport key Public key transport keyPublic key transport key Symmetric key agreement key (also, Symmetric key agreement key (also,

key wrapping key)key wrapping key)

TypesTypes

Private ephemeral key agreement Private ephemeral key agreement keykey

Public ephemeral key agreement keyPublic ephemeral key agreement key Symmetric authorization keysSymmetric authorization keys Private authorization keyPrivate authorization key Public authorization keyPublic authorization key

General Terms in Key General Terms in Key ManagementManagement

Key registrationKey registration Key revocationKey revocation Key transportKey transport Key updateKey update Key derivationKey derivation Key confirmationKey confirmation Key establishmentKey establishment Key agreementKey agreement

TermsTerms

Registration authorityRegistration authority Security domainSecurity domain Self-signed certificateSelf-signed certificate

Valuable Information in Valuable Information in Addition to Cryptographic KeysAddition to Cryptographic Keys

Domain parametersDomain parameters Initialization vectors, shared secrets, Initialization vectors, shared secrets,

RNG seeds, nonces, random numbersRNG seeds, nonces, random numbers Intermediate resultsIntermediate results Key control informationKey control information PasswordsPasswords Audit informationAudit information

CryptoperiodsCryptoperiods

Time span during which a specific key is Time span during which a specific key is authorized for use by legitimate entities, or authorized for use by legitimate entities, or the keys for a given system will remain in the keys for a given system will remain in effect. A good cryptoperiodeffect. A good cryptoperiod Limits amount of information protected by a Limits amount of information protected by a

given key from disclosuregiven key from disclosure Limits amount of exposure if a single key is Limits amount of exposure if a single key is

compromisedcompromised Limits use of particular algorithm to its estimated Limits use of particular algorithm to its estimated

effective lifetimeeffective lifetime limits time available to penetrate physical, limits time available to penetrate physical,

procedural, and logical access mechanisms that procedural, and logical access mechanisms that protect a keyprotect a key

Risk Factors to Consider for Risk Factors to Consider for CryptoperiodsCryptoperiods

Strength of cryptographic implementationsStrength of cryptographic implementations Operating environment, secure limited Operating environment, secure limited

access, open office or public terminalaccess, open office or public terminal Volume of information or transactionsVolume of information or transactions Security objectiveSecurity objective Re-keying methodRe-keying method Number of nodes sharing the key/copies of Number of nodes sharing the key/copies of

the keythe key Threat to informationThreat to information

Other Factors Affecting Other Factors Affecting CryptoperiodsCryptoperiods

Communication vs StorageCommunication vs Storage E.g., keys used for online transactions are E.g., keys used for online transactions are

likely to have smaller cryptoperiodslikely to have smaller cryptoperiods Keys used for storage will have higher, as cost Keys used for storage will have higher, as cost

of re-encryption is highof re-encryption is high Cost of Key Revocation and ReplacementCost of Key Revocation and Replacement

Changing keys can be an expensive processChanging keys can be an expensive process Encryption of large databasesEncryption of large databases Revocation of large number of keysRevocation of large number of keys Expensive security measures are justified for such Expensive security measures are justified for such

cases as the cryptoperiod can be made highcases as the cryptoperiod can be made high

Factors Affecting Public Factors Affecting Public KeysKeys

Private keys may have longer cryptoperiods Private keys may have longer cryptoperiods than public-keys when used for confidentialitythan public-keys when used for confidentiality

When used for challenge (dynamic) When used for challenge (dynamic) authentication both public and private keys authentication both public and private keys can have the same cryptoperiodcan have the same cryptoperiod

When used for digital signatures public keys When used for digital signatures public keys can have longer cryptoperiods than private can have longer cryptoperiods than private keys as they will be necessary to verify keys as they will be necessary to verify certificatescertificates

Cryptoperiods for Different Cryptoperiods for Different KeysKeys

Private signature key (public-private keys)Private signature key (public-private keys) 1-3years1-3years

Public signature verification keysPublic signature verification keys Symmetric authentication keySymmetric authentication key

2-3 years2-3 years Private authentication keyPrivate authentication key

1-2years1-2years Public authentication keysPublic authentication keys

1-2years1-2years Symmetric data encryption keySymmetric data encryption key

3years3years

Cryptoperiods for Different Cryptoperiods for Different KeysKeys

Symmetric and asymmetric random Symmetric and asymmetric random number generation keysnumber generation keys Depends on the RNG techniqueDepends on the RNG technique

Symmetric master keySymmetric master key 1 year1 year

Private and Public key transport keysPrivate and Public key transport keys Private 2years, public 1-2 yearsPrivate 2years, public 1-2 years

Symmetric key agreement key (also, key Symmetric key agreement key (also, key wrapping key)wrapping key) 1-2years1-2years

Cryptoperiods for Different Cryptoperiods for Different KeysKeys

Private and public ephemeral key Private and public ephemeral key agreement keyagreement key Time required to complete the key Time required to complete the key

agreement protocolagreement protocol Symmetric authorization keysSymmetric authorization keys

2years2years Private and Public authorization keysPrivate and Public authorization keys

2years2years

Other ParametersOther Parameters

Domain parameters stay for the cryptoperiodDomain parameters stay for the cryptoperiod IV is associated with the information and IV is associated with the information and

stays as long as the information is heldstays as long as the information is held Shared secrets are destroyed as soon as the Shared secrets are destroyed as soon as the

necessary key derivations are completenecessary key derivations are complete RNG seeds are destroyed immediatelyRNG seeds are destroyed immediately Intermediate results are destroyed Intermediate results are destroyed

immediatelyimmediately

Algorithms, Key Sizes and Algorithms, Key Sizes and StrengthsStrengths

Factors to be Considered For Factors to be Considered For Design of New SystemDesign of New System

Sensitivity of information and system lifetimeSensitivity of information and system lifetime Algorithm selectionAlgorithm selection System design wrt performance and securitySystem design wrt performance and security Pre-implementation evaluationPre-implementation evaluation TestingTesting TrainingTraining System implementation and transitionSystem implementation and transition Post-implementation evaluationPost-implementation evaluation