License	BSD-style
Maintainer	Vincent Hanquez <vincent@snarc.org>
Stability	experimental
Portability	unknown
Safe Haskell	None
Language	Haskell98

Data.X509.Validation

Contents

Failed validation types
Validation configuration types
Validation
Cache
Cache for validation
Simple instances of cache mechanism

Description

X.509 Certificate checks and validations routines

Follows RFC5280 / RFC6818

Synopsis

Documentation

type ServiceID = (HostName, ByteString) Source

identification of the connection consisting of the fully qualified host name (e.g. www.example.com) and an optional suffix.

The suffix is not used by the validation process, but is used by the optional cache to identity certificate per service on a specific host. For example, one might have a different certificate on 2 differents ports (443 and 995) for the same host.

for TCP connection, it's recommended to use: :port, or :service for the suffix.

type HostName = String Source

newtype Fingerprint Source

Fingerprint of a certificate

Constructors

Fingerprint ByteString

Instances

Eq Fingerprint Source
Show Fingerprint Source
Byteable Fingerprint Source

Failed validation types

data FailedReason Source

Possible reason of certificate and chain failure

Constructors

UnknownCriticalExtension	certificate contains an unknown critical extension
Expired	validity ends before checking time
InFuture	validity starts after checking time
SelfSigned	certificate is self signed
UnknownCA	unknown Certificate Authority (CA)
NotAllowedToSign	certificate is not allowed to sign
NotAnAuthority	not a CA
AuthorityTooDeep	Violation of the optional Basic constraint's path length
NoCommonName	Certificate doesn't have any common name (CN)
InvalidName String	Invalid name in certificate
NameMismatch String	connection name and certificate do not match
InvalidWildcard	invalid wildcard in certificate
LeafKeyUsageNotAllowed	the requested key usage is not compatible with the leaf certificate's key usage
LeafKeyPurposeNotAllowed	the requested key purpose is not compatible with the leaf certificate's extended key usage
LeafNotV3	Only authorized an X509.V3 certificate as leaf certificate.
EmptyChain	empty chain of certificate
CacheSaysNo String	the cache explicitely denied this certificate
InvalidSignature SignatureFailure	signature failed

Instances

Eq FailedReason Source
Show FailedReason Source

data SignatureFailure Source

Various failure possible during signature checking

Constructors

SignatureInvalid	signature doesn't verify
SignaturePubkeyMismatch	algorithm and public key mismatch, cannot proceed
SignatureUnimplemented	unimplemented signature algorithm

Instances

Eq SignatureFailure Source
Show SignatureFailure Source

Validation configuration types

data ValidationChecks Source

A set of checks to activate or parametrize to perform on certificates.

It's recommended to use defaultChecks to create the structure, to better cope with future changes or expansion of the structure.

Constructors

ValidationChecks

Fields

checkTimeValidity :: Bool: check time validity of every certificate in the chain. the make sure that current time is between each validity bounds in the certificate
checkAtTime :: Maybe DateTime: The time when the validity check happens. When set to Nothing, the current time will be used
checkStrictOrdering :: Bool: Check that no certificate is included that shouldn't be included. unfortunately despite the specification violation, a lots of real world server serves useless and usually old certificates that are not relevant to the certificate sent, in their chain.
checkCAConstraints :: Bool: Check that signing certificate got the CA basic constraint. this is absolutely not recommended to turn it off.
checkExhaustive :: Bool: Check the whole certificate chain without stopping at the first failure. Allow gathering a exhaustive list of failure reasons. if this is turn off, it's absolutely not safe to ignore a failed reason even it doesn't look serious (e.g. Expired) as other more serious checks would not have been performed.
checkLeafV3 :: Bool: Check that the leaf certificate is version 3. If disable, version 2 certificate is authorized in leaf position and key usage cannot be checked.
checkLeafKeyUsage :: [ExtKeyUsageFlag]: Check that the leaf certificate is authorized to be used for certain usage. If set to empty list no check are performed, otherwise all the flags is the list need to exists in the key usage extension. If the extension is not present, the check will pass and behave as if the certificate key is not restricted to any specific usage.
checkLeafKeyPurpose :: [ExtKeyUsagePurpose]: Check that the leaf certificate is authorized to be used for certain purpose. If set to empty list no check are performed, otherwise all the flags is the list need to exists in the extended key usage extension if present. If the extension is not present, then the check will pass and behave as if the certificate is not restricted to any specific purpose.
checkFQHN :: Bool: Check the top certificate names matching the fully qualified hostname (FQHN). it's not recommended to turn this check off, if no other name checks are performed.

Instances

Eq ValidationChecks Source
Show ValidationChecks Source
Default ValidationChecks Source

data ValidationHooks Source

A set of hooks to manipulate the way the verification works.

BEWARE, it's easy to change behavior leading to compromised security.

Constructors

ValidationHooks

Fields

hookMatchSubjectIssuer :: DistinguishedName -> Certificate -> Bool: check the the issuer DistinguishedName match the subject DistinguishedName of a certificate.
hookValidateTime :: DateTime -> Certificate -> [FailedReason]: validate that the parametrized time valide with the certificate in argument
hookValidateName :: HostName -> Certificate -> [FailedReason]: validate the certificate leaf name with the DNS named used to connect
hookFilterReason :: [FailedReason] -> [FailedReason]: user filter to modify the list of failure reasons

Instances

Default ValidationHooks Source

defaultChecks :: ValidationChecks Source

Default checks to perform

The default checks are: * Each certificate time is valid * CA constraints is enforced for signing certificate * Leaf certificate is X.509 v3 * Check that the FQHN match

defaultHooks :: ValidationHooks Source

Default hooks in the validation process

Validation

validate Source

Arguments

:: HashALG	the hash algorithm we want to use for hashing the leaf certificate
-> ValidationHooks	Hooks to use
-> ValidationChecks	Checks to do
-> CertificateStore	The trusted certificate store for CA
-> ValidationCache	the validation cache callbacks
-> ServiceID	identification of the connection
-> CertificateChain	the certificate chain we want to validate
-> IO [FailedReason]	the return failed reasons (empty list is no failure)

X509 validation

the function first interrogate the cache and if the validation fail, proper verification is done. If the verification pass, the add to cache callback is called.

validateDefault Source

Arguments

:: CertificateStore	The trusted certificate store for CA
-> ValidationCache	the validation cache callbacks
-> ServiceID	identification of the connection
-> CertificateChain	the certificate chain we want to validate
-> IO [FailedReason]	the return failed reasons (empty list is no failure)

Validate using the default hooks and checks and the SHA256 mechanism as hashing mechanism

getFingerprint Source

Arguments

:: (Show a, Eq a, ASN1Object a)
=> SignedExact a	object to fingerprint
-> HashALG	algorithm to compute the fingerprint
-> Fingerprint	fingerprint in binary form

Get the fingerprint of the whole signed object using the hashing algorithm specified

Cache

Cache for validation

data ValidationCacheResult Source

The result of a cache query

Constructors

ValidationCachePass	cache allow this fingerprint to go through
ValidationCacheDenied String	cache denied this fingerprint for further validation
ValidationCacheUnknown	unknown fingerprint in cache

Instances

Eq ValidationCacheResult Source
Show ValidationCacheResult Source

type ValidationCacheQueryCallback Source

Arguments

= ServiceID	connection's identification
-> Fingerprint	fingerprint of the leaf certificate
-> Certificate	leaf certificate
-> IO ValidationCacheResult	return if the operation is succesful or not

Validation cache query callback type

type ValidationCacheAddCallback Source

Arguments

= ServiceID	connection's identification
-> Fingerprint	fingerprint of the leaf certificate
-> Certificate	leaf certificate
-> IO ()

Validation cache callback type

data ValidationCache Source

All the callbacks needed for querying and adding to the cache.

Constructors

ValidationCache
Fields cacheQuery :: ValidationCacheQueryCallback cache querying callback cacheAdd :: ValidationCacheAddCallback cache adding callback

Instances

Default ValidationCache Source

Simple instances of cache mechanism

exceptionValidationCache :: [(ServiceID, Fingerprint)] -> ValidationCache Source

create a simple constant cache that list exceptions to the certification validation. Typically this is use to allow self-signed certificates for specific use, with out-of-bounds user checks.

No fingerprints will be added after the instance is created.

The underlying structure for the check is kept as a list, as usually the exception list will be short, but when the list go above a dozen exceptions it's recommended to use another cache mechanism with a faster lookup mechanism (hashtable, map, etc).

Note that only one fingerprint is allowed per ServiceID, for other use, another cache mechanism need to be use.

tofuValidationCache Source

Arguments

:: [(ServiceID, Fingerprint)]	a list of exceptions
-> IO ValidationCache

Trust on first use (TOFU) cache with an optional list of exceptions

this is similar to the exceptionCache, except that after each succesfull validation it does add the fingerprint to the database. This prevent any further modification of the fingerprint for the remaining