About PKI Certificates

Dartmouth College PKI Lab

X.509 Certificate Defined

A type that binds an entity's distinguished name to a public key with a digital signature. This type is defined in the Internet X.509 Public Key Infrastructure (PKIX) Certificate and CRL Profile. This type also contains the distinguished name of the certificate issuer (the signer), an issuer-specific serial number, the issuer's signature algorithm identifier, a validity period, and extensions also defined in that document.

X.509 Certificate Defined 2

Data associated with a private key and containing a public key that provides information about:

• Identities of the issuer and subject

• Certificate validity dates and CRL location

• Certificate intended uses

• Serial number

• Other certificate information

X.509 Certificate Format• version• serialNumber • signature• issuer• validity• subject • subjectPublicKeyInfo• issuerUniqueIdentifier• subjectUniqueIdentifier• Extensions

Certificate information is contained in ASN.1 structures.

Certificate Encodings

• DER is a binary encoding of the X.509 ASN.1 structures.

• PEM is the base 64 encoded version of DER. (For situations where binary format won’t work.)

• Text is a human-readable version of the ASN.1 structures.

PEM Example -----BEGIN CERTIFICATE-----

MIIEbDCCA1SgAwIBAgICBAEwDQYJKoZIhvcNAQEFBQAwdzETMBEGCgmSJomT8ixk ARkWA2VkdTEZMBcGCgmSJomT8ixkARkWCWRhcnRtb3V0aDELMAkGA1UEBhMCVVMx GjAYBgNVBAoTEURhcnRtb3V0aCBDb2xsZWdlMRwwGgYDVQQDExNEYXJ0bW91dGgg Q2VydEF1dGgxMB4XDTAzMTAyNDE1MDg1OFoXDTAzMTAyNDE5MDg1OFowgaIxEzAR BgoJkiaJk/IsZAEZFgNlZHUxGTAXBgoJkiaJk/IsZAEZFglkYXJ0bW91dGgxCzAJ BgNVBAYTAlVTMRowGAYDVQQKExFEYXJ0bW91dGggQ29sbGVnZTEZMBcGA1UEAxMQ TWFyayBKLiBGcmFua2xpbjEsMCoGCSqGSIb3DQEJARYdTWFyay5KLkZyYW5rbGlu QERhcnRtb3V0aC5lZHUwgZ8wDQYJKoZIhvcNAQEBBQADgY0AMIGJAoGBAK2Xsb+0 +ENqEwgu15Sthv47iKJ89O1ci0TLdbVYoFV92wDykX68+m2Z0NSBiM+mQqjDk8c6 USnAvwDZUtMVK5CU9kf9/hiCXmVxbFLgsqbpVEPzc83SGQ3fS70PuFeu00MdTRI6 +thtwTF/n7ZfGFc2XGTKXMnwqCh8cbOP7H5NAgMBAAGjggFYMIIBVDARBglghkgB hvhCAQEEBAMCBaAwDgYDVR0PAQH/BAQDAgXgMIGiBgNVHSAEgZowgZcwgZQGCisG AQQBQQIBAQEwgYUwPQYIKwYBBQUHAgIwMTAYFhFEYXJ0bW91dGggQ29sbGVnZTAD AgEBGhVEYXJ0bW91dGggQ29sbGVnZSBDUFMwRAYIKwYBBQUHAgEWOGh0dHA6Ly93 d3cuZGFydG1vdXRoLmVkdS9+cGtpbGFiL0RhcnRtb3V0aENQU180U2VwMDMucGRm MCgGA1UdEQQhMB+BHU1hcmsuSi5GcmFua2xpbkBEYXJ0bW91dGguZWR1MB8GA1Ud IwQYMBaAFD/A1senTwB+7waZZ2y8lh5No3cSMD8GCCsGAQUFBwEBBDMwMTAvBggr BgEFBQcwAYYjaHR0cDovL2NvbGxlZ2VjYS5kYXJ0bW91dGguZWR1L29jc3AwDQYJ KoZIhvcNAQEFBQADggEBAB5+LvOPrCt6s6Hvba5a7WENTLxhh7r2KUZIDH7Y1PJ8 cUN5EfKAUoT00walcTIqCfexLpWJMk38oF4gTMwk3sabNEjfQwmdmsJSh2R6eBDL d658t94DpGxXw2U3rzDzFDc4lozK9cBn9GRt4w3py31Bz2DDzc4mjscEid44AV3V hLhI0ZqlWrqWWutW1Dugqol8A6APVGMjhZsYS5fFUe88LdvZgnb9UpDcOAPUoeN5 Rvl/aibNweyCBFU/MqII0Yxf1wrc+wg0R2gy+WaVqyK05ddwxwVJ94aZmAHGL6zO 7FjPU9XwLGBQfHbnbtfRZUech+ZQhjLlpXyYxRQ1KgM=

-----END CERTIFICATE-----

Text ExampleCertificate: Data:

Version: v3 Serial Number: 0x401 Signature Algorithm: SHA1withRSA - 1.2.840.113549.1.1.5 Issuer: CN=Dartmouth CertAuth1,O=Dartmouth College,C=US,DC=dartmouth,DC=edu Validity:

Not Before: Friday, October 24, 2003 11:08:58 AM EDT America/New_York Not After: Friday, October 24, 2003 3:08:58 PM EDT America/New_York

Subject: E=Mark.J.Franklin@Dartmouth.edu,CN=Mark J. Franklin,O=Dartmouth College,C=US,DC=dartmouth,DC=edu

Subject Public Key Info: Algorithm: RSA - 1.2.840.113549.1.1.1 Public Key:

Exponent: 65537 Public Key Modulus: (1024 bits) :

AD:97:B1:BF:B4:F8:43:6A:13:08:2E:D7:94:AD:86:FE: 3B:88:A2:7C:F4:ED:5C:8B:44:CB:75:B5:58:A0:55:7D: DB:00:F2:91:7E:BC:FA:6D:99:D0:D4:81:88:CF:A6:42: A8:C3:93:C7:3A:51:29:C0:BF:00:D9:52:D3:15:2B:90: 94:F6:47:FD:FE:18:82:5E:65:71:6C:52:E0:B2:A6:E9: 54:43:F3:73:CD:D2:19:0D:DF:4B:BD:0F:B8:57:AE:D3: 43:1D:4D:12:3A:FA:D8:6D:C1:31:7F:9F:B6:5F:18:57: 36:5C:64:CA:5C:C9:F0:A8:28:7C:71:B3:8F:EC:7E:4D

Extensions: Identifier: Netscape Certificate Type - 2.16.840.1.113730.1.1

Critical: no Certificate Usage:

SSL Client Secure Email

Identifier: Key Usage: - 2.5.29.15 Critical: yes Key Usage:

Digital Signature Non Repudiation Key Encipherment

Identifier: CertificatePolicies - 2.5.29.32

CertificateViewer

Example

Certificate Revocation List (CRL) Defined

A type that contains information about certificates whose validity an issuer has prematurely revoked. The information consists of an issuer name, the time of issue, the next scheduled time of issue, a list of certificate serial numbers and their associated revocation times, and extensions. The CRL is signed by the issuer.

Certificate Revocation List (CRL) Defined 2

A secured list of no longer trusted certificates provided by a Certificate Authority so applications can reject otherwise valid certificates that are compromised or otherwise invalid before their validity period expires.

• Issued periodically or as needed.• Checked by applications at certificate verification time.• OCSP protocol provides an alternative which can be an

online service.

CRL Format

• version• signature• issuer• thisUpdate• nextUpdate• revokedCertificates• crlEntryExtensions• crlExtensions

CRL Example

CRL Example 2

Certificate Viewers• Windows (invoked from IE, desktop, other

applications)• Mozilla/Thunderbird (invoked from Preferences

in Mozilla or Account Options in Thunderbird)• Other applications

Demos of Certificate ViewersWindowsMozilla

About PKI Key Stores

Dartmouth College PKI Lab

Key Store Defined• Protected “vault” to hold user’s private key

with their copy of their x.509 certificate• A function of their client computer and

software• Should be locally password protected• Should be encrypted and/or protected by

specialized hardware• May be provided by OS or by application(s)• May hold the only copy of a private key

Key Store Anatomy (first look before we launch into details)

Key Store Interfaces

• Microsoft Windows CAPI

• RSA PKCS#11

• RSA PKCS#12

• Java Keystore

• Application specific

Browsers and Key Stores

• Browsers provide one of the most common ways to access key stores

• GUI for key generation and certificate enrollment• Viewing and manipulating certificates and keys• Import/export

Mozilla/Netscape/FireFox does PKCS#11

Internet Explorer/Windows does CAPI

Key Store Types

• “Software”– Keys encrypted in a file

• “Hardware”– Keys stored on specialized hardware tokens

OS Key Stores

• CAPI: Microsoft Windows CryptoAPI

• “Keychain” from Apple

Many Windows applications use CAPI; others have their own key store.

“Software” Key Store

• Stores certificates and encrypted keys on the local computer’s file system

• Encryption is password protected• Relatively vulnerable to key theft (depending on

implementation)• Requires exporting and importing to use the key

on another computer or in a different key store on the same computer

All PKI applications support this type of key store – for some it is the only type supported.

“Hardware” Key Store• Stores certificates and keys in special purpose

hardware (typically USB token or smart card and reader)

• Much higher assurance - the key cannot be used without the user’s password, but still not unbreakable

• Allows easy private key mobility between computers and applications

• Two-factor security (need token plus password to do anything) makes hardware key stores much more secure than software key stores

PKCS#11• Standard developed by RSA to provide

applications with a key store and PKI cryptographic functions

http://www.rsasecurity.com/rsalabs/pkcs/pkcs-11/

• Used by Mozilla on all OSes (even Windows)• Has a lower-level API for plugging in different

implementations (enables hardware tokens)• Open source implementations available• Similar to MS CAPI – unfortunately MS opted

to not support PKCS#11

Microsoft CAPI (AKA CryptoAPI)• Microsoft Windows “standard” API for providing PKI

functionality to applicationshttp://msdn.microsoft.com/library/en-us/security/security/cryptography_portal.asp?

• Provides:– Key store function– Cryptographic operations using the key store and certificate– GUI for managing certificates and keys– Facilities to create, import, and export certificates and keys

• Cryptographic Service Provider (CSP) layer allows 3rd party software, token, and smartcard solutions

• Microsoft’s software key store CSP has some issues

Key Store Anatomy (revisited now that we are familiar with the pieces)

Application Key Stores

• Some applications don’t use either CAPI or PKCS#11

• Adds undesirable complexity for average end user• Incompatible with hardware keys (since they can

only support PKCS#11 and CAPI/CSP interfaces)• Require exporting and importing certificates/keys• AOL AIM has its own key store• Java keystores becoming more utilized

How PKI Uses Passwords• Passwords protect local key stores

• Stored and managed locally by the user

• Never stored on servers (an important feature – passwords on servers and traversing a network are more vulnerable)

• User provides the password to “unlock” their private key – all other operations use asymmetric key cryptography

User Accounts

• Windows CAPI stores software keys in each user’s profile

• If user accounts are secure, then CAPI keys are protected by the Windows logon security

PKCS#7 and PKCS#12• More RSA standards• No awards for imaginative names…• PKCS#7 is general syntax for data that may have

cryptography applied to ithttp://www.rsasecurity.com/rsalabs/pkcs/pkcs-7/index.html

• PKCS#12 specifies secure containers for transporting PKI certificates with private keys

http://www.rsasecurity.com/rsalabs/pkcs/pkcs-12/index.html