Public Key InfrastructuresPublic Key Infrastructures

Chapter 6Private KeysPrivate Keys

Cryptography and ComputeralgebraProf Dr Johannes BuchmannProf. Dr. Johannes BuchmannDr. Alexander Wiesmaier

Personal Security Environment (PSE)

H t t i t k ?How to store private keys?

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Realisation of PSEs : Tokens

Secure storing of private keysSecure storing of private keys

in Software in Hardware

PKCS#12Application specific

(e.g. Netscape)Java KeyStore SmartcardUSB-Token

HardwareSecurityM d leyS o e Module(HSM)

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Token properties

Compatibility

PortabilityPortability

Availability

Access protection

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PKCS#12

Software based PSESoftware based PSE

F t f t t d t iFormat for secure transport and storing

Most typical format for software PSEs

Available at:http://www rsa com/rsalabs/node asp?id 2138http://www.rsa.com/rsalabs/node.asp?id=2138

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PKCS#12: Modes

Public Key Privacy Mode:Encryption with a symmetric key. This symmetric key is encrypted with the public key of the receiver.

P d P i M dPassword Privacy Mode:Encryption with a symmetric key, which is derived from

da password.Public Key Integrity Mode:

Si d ith i t k Th i if thSigned with a private key. The receiver can verify the message.

Password Integrity Mode:Password Integrity Mode:A MAC is calculated which can be verified by the receiver

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receiver.

PKCS#12: ASN.1

PFX ::= SEQUENCE {version INTEGER {v3(3)}(v3,...),authSafe ContentInfo,macData MacData OPTIONAL

}

AuthenticatedSafe ::= SEQUENCE OF ContentInfo-- Data if unencryptedyp-- EncryptedData if password-encrypted-- EnvelopedData if public key-encryptedp p y yp

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PKCS#12: Structure

C t tI f

AuthenticatedSafe

ContentInfo

Plain data

EncryptedEncrypted data

Enveloped data

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Java KeyStore

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Java Keystores

Implementation of the KeyStore Class

Two types:JKSJKS

Proprietary algorithmsWeak encr ptionWeak encryption

JCEKSSt d d l ithStandard algorithmsStrong encryptionP t f th JCE (J C t h E t i )Part of the JCE (Java Cryptography Extensions)Since Java 1.4

10Easy Administration with keytool

KeyStore example

keytool -genkey -alias test -keyalg RSA-keysize 1024 -keypass 123456keysize 1024 keypass 123456-storepass 123456 -keystore test.ks

Run: ../BatchFiles/keytool.bat

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Application specific

Netscape FamilyMozilla, Firefox, Thunderbird, SeaMonkey

Through Software Security ModuleThe standard implementation is proprietaryThe format for the import is PKCS#12

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Private key import in Firefox

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Private key access in Firefox

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Application specific

Windows Internet Explorer, Outlook/Express

The standard implementation is proprietaryThrough Cryptographic Service ProviderThe format for the import is PKCS#12

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Private key import in Windows

cs_student.p12

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Private key access in Windows

cs_student.p12

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Hardware Security Module

Secure storage and use of keys

(Pseudo)random number generation(Pseudo)random number generation

Key pair generation

Key archiving

Encryption / decryptionEncryption / decryption

Generating / verifying signatures

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Acceleration for cryptographic schemes (e.g. TLS)

Hardware Security Module

Protect the keys against

Mechanical attacksMechanical attacks

Temperature attacks

Manipulation of the voltage

Chemical attacksChemical attacks

The keys are destroyed in case of danger

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Hardware Security Module

But…

Keys can be accidentally destroyedKeys can be accidentally destroyed

e.g. due to mechanical influence during transport

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Network Attached HSM

Shared HSM

SpeedSpeed

Availability

Robustness

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Smartcards

Secure key storing and use

Ke pair generation (not all)Key pair generation (not all)

Calculation of digital signaturesCalculation of digital signatures

Decryptionyp

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Access over PKCS#11

Interface to the HSM

Support functions like:Change PIN, Sign, Decrypt, Write certificateg , g , yp ,

But:But:Some functions are not supported (e.g. change PUK)Different libraries are needed for supporting different cardsDifferent libraries are needed for supporting different cards and readers.

Available at:http://www.rsa.com/rsalabs/node.asp?id=2133

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http://www.rsa.com/rsalabs/node.asp?id 2133

PKCS#15

Specifies the structure of the filesystem in the chip card

E di t i th d i li tiEvery directory in the card is an application

Pointers to cryptographic objects (ODF)y g j ( )

Private Key

Public Key

Certificate

There is a newer specification based on it: ISO 7816-15

Available at:

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http://www.rsa.com/rsalabs/node.asp?id=2141

Structure PKCS#15

MasterFile(MF)

(Root directory)(MF)

DescriptorDF(PKCS#15)

FurtherDFs/EFs

UserdataEF (DIR)

(Meta data)

TokenInfoADFCDFPrKDFODF

Object Directory File: Pointers to directories:PrivateKey Data, Certificate Data, Authentication Data (PIN) and

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y , , ( )Token Information (Serial number)

E4 NetKey (TeleSec)

E4 evaluated (according to ITSEC)

Global files (serial number, etc.)

SigG applicationS gG app cat o

Pre-keyd with one key-pair according to SigG

(Signature Act)

NetKey applicationy pp

3 key pairs (pre-keyed)

Null-PIN scheme (patented)

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Java Cards

No filesystem but applets

JCRE (J C d R ti E i t)JCRE (Java Card Runtime Environment)

manages:g

the resources of the card

the communication with the outside world

the execution of the appletspp

controls:

the compliance with the security limitations

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Java Cards

Like normal Java code, but without:

Long do ble floatLong, double, float

Characters and strings

Multidimensional arrays

ThreadsThreads

Object serialization und cloning

Dynamic loading of classes (like drivers)

Security ManagerSecurity Manager

Garbage Collector not always present

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Life cycle of private keys

Generation

Backup

Generation

Storing Recovery

Transport

Usestart state

state

Destruction

state

end state

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Destruction

Life cycle of private keys

GenerationGenerationBackup

GenerationGeneration

Storing Recovery

Transport

appropriate parameters

Use

appropriate parameters

secure random number generator

Destruction

generator

shielding against eavesdropping

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Destruction•…

Life cycle of private keys

Generation

Backup

Generation

StoringStoring Recovery

Transport

persistent storing

Use

persistent storing

deletion from the generator

Destruction

appropriate access protection

…

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Destruction

Life cycle of private keys

Generation

Backup

Generation

Storing Recovery

TransportTransportcorrect receiver

Use

correct receiver

guaranteed delivery

Destruction

appropriate transport security mechanisms…

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Destruction

Life cycle of private keys

Generation

Backup

Generation

Storing Recovery

Transport

easy for the authorised users

UseUse

easy for the authorised users

impossible for the unauthorised users

Destruction

users

protection of the private key

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Destruction…

Life cycle of private keys

Generation

Backup

Generation

Storing Recovery

Transport

unrecoverable

Use

unrecoverable

easy for authorised users

DestructionDestruction

impossible for unauthorised users

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DestructionDestruction•…

Life cycle of private keys

Generation

BackupBackupGeneration

Storing Recovery

Transport

persistent storing

Use

persistent storing

only for certain keys

Destruction

appropriate access protection

…

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Destruction

Life cycle of private keys

Generation

Backup

Generation

Storing RecoveryRecovery

Transport

correct reestablishment

Use

correct reestablishment

easy for authorised users

Destruction

impossible for unauthorised users

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Destruction…

Life cycle of private keys

Example 1: User generates keys

Here: PGP

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Generation

3838

Generation

3939

Generation

4040

Generation

4141

Generation

4242

Generation

4343

Generation

4444

Generation

4545

Storing

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Transport

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Transport

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Transport

File contentsFile contents

/C tifi t /T t U t../Certificates/Test User.cxt

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Use

5050

Use

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Destruction

5252

Destruction

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Destruction

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Backup

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Backup

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Backup

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Backup

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Recovery

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Recovery

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Recovery

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Life cycle of private keys

Example 2: TC generates keys

H TUD C dHere: TUD Card

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Generation

The manufacturer creates the keys

input

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output

Storing

C t i th i t kContains the private key

A file exists that holds the private key.

Security condition:

PSO (Perform Security Operation) after

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PSO (Perform Security Operation) after PIN has been correctly given.

Transport

By snail mail

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Use

First Use detectionst Use detect o

Null-PIN technique

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Use

PIN-Entry

necessary

for PSO

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Use

Set PINSee PUKDownload certificate

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Destruction

Physical destruction of the card.

high temperature, etc…g p

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Backup

Each encryption key is stored in a PKCS#12 file

input

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output

Life cycle of private keys

Example 3: User generates keys

H J k t lHere: Java keytool

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Generate

keytool -genkey -keyalg RSA -keystore keystore.ks -alias myalias

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Store

keytool -genkey -keyalg RSA -keystore keystore.ks -alias myalias

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Transport

Th k i l d t th li t idThe key is already at the client side.

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Use

In order to use the private key, the public key is certified by a CA.

Thawte example

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Hi! Please use your browser to go to the following URL: https://www.thawte.com/cgi/enroll/personal/step8.exe Once you h t d f ll t th b dd thave connected successfully to the above address, you must copy and paste the "probe" and "ping" values below into the appropriate text boxes:appropriate text boxes:Probe: value Ping: valueYou should save this message until you have completed the enrollment process, just in case. But you MUST go to the above URL within 24 hours or we will delete your request informationURL within 24 hours, or we will delete your request information and you'll have to start over! If you have problems completing the above please contact our support team by going to thethe above please contact our support team by going to the following URL: https://www.thawte.com/cgi/support/contents.exeRegards,

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The thawte team thawte Certification

8383 8484

85 8686

87 88

email address

89 90

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keytool -certreq -keystore keystore.ks -file csr.txt -alias myalias

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-----BEGIN NEW CERTIFICATE REQUEST-----MIIBrDCCARUCAQwbDELMAkGA1UEBhMCREUxDjAMBgNVBTBUhlc3NlMRIwEAYDVQQHEwlEYXJtN57qbnyAfAAAAAAAQQ q yc3RhZHQxDDKBgNVATA1RVRDEMMAoGA1UECxMDQ0RDMRwGwYDVQQDExRWY5nZWxpcyBLYXJhN57qbnyAfAAAAAAAdHNpb2xpcznzANBqhkiG9w0BAQEFAAOBjQAwgYkCgYEAroJdHNpb2xpcznzANBqhkiG9w0BAQEFAAOBjQAwgYkCgYEAroJITHFBR5orQ9dB4qkP/gMhS1hCNiowdM2CrJINiowdM2CCCCE+Qrzut77pzzjlEBLQeeMC0Q88LF8tTJfFoUKdGni/PAAiOPHxvNXFFH0YZs4/P7gXMAX+9eEgGNiowdM2CrJINiowdM2CCCCENXFFH0YZs4/P7gXMAX+9eEgGNiowdM2CrJINiowdM2CCCCEjL2ig7PyQlkGGwIbvxYQmEX2TKk9tKWqCvFjl6BKTjIIjErmgolyi79dk3Cdwx26Z8CAwEAAaAANiowdM2CrJINiowdM2CCCCEEEMA0GCSqGSIb3DEBBAUAAGBAI baheW+lVaDdRN57qbn Af3MA0GCSqGSIb3DEBBAUAAGBAIvbaheW+lVaDdRN57qbnyAf3qqxD2GcjmBcCcO8v3TN9zc4mSENiowdM2CrJINiowdM2CCCCpXXTFQg4UqO0urJINiowdM2CtrPzlEtORJNtoxxiRLHp9+LLNXnER43nYvcLZ/QIChlfIX6KiPrJINiowdM2CrJINiowdM2CCCCElr81bvYRq6G/bGxrz4K55c17UIqPtlGN7yQEDxYZ5e+-----END NEW CERTIFICATE REQUEST-----

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The user receives a URL that contains thecertificate inside a PKCS#7 structure

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keytool -import -file test crt -alias myalias -trustcacerts -keystore keystore kskeytool import file test.crt alias myalias trustcacerts keystore keystore.ks

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Destruction

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Backup

A simple copy of the file to:CDa CD

a USB stickan external hard disc… or similar… or similar

The password may be changedThe password may be changed.

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Recovery

Recovery from the copy location.

Password is needed.

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