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Code Issues Releases Wiki Activity

Kotlin conversion: SignatureValidator

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Paul Schaub 2023-10-25 19:07:52 +02:00
parent 733d5d6b82
commit e9d8ddc57b
Signed by: vanitasvitae
GPG key ID: 62BEE9264BF17311
3 changed files with 704 additions and 681 deletions
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681
pgpainless-core/src/main/java/org/pgpainless/signature/consumer/SignatureValidator.java
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@ -1,681 +0,0 @@
// SPDX-FileCopyrightText: 2021 Paul Schaub <vanitasvitae@fsfe.org>
//
// SPDX-License-Identifier: Apache-2.0
package org.pgpainless.signature.consumer;
import java.util.Arrays;
import java.util.Collections;
import java.util.Date;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.concurrent.ConcurrentHashMap;
import org.bouncycastle.bcpg.sig.KeyFlags;
import org.bouncycastle.bcpg.sig.NotationData;
import org.bouncycastle.bcpg.sig.SignatureCreationTime;
import org.bouncycastle.openpgp.PGPException;
import org.bouncycastle.openpgp.PGPPublicKey;
import org.bouncycastle.openpgp.PGPSignature;
import org.bouncycastle.openpgp.PGPSignatureList;
import org.bouncycastle.openpgp.PGPSignatureSubpacketVector;
import org.bouncycastle.openpgp.PGPUserAttributeSubpacketVector;
import org.pgpainless.algorithm.HashAlgorithm;
import org.pgpainless.algorithm.KeyFlag;
import org.pgpainless.algorithm.PublicKeyAlgorithm;
import org.pgpainless.algorithm.SignatureSubpacket;
import org.pgpainless.algorithm.SignatureType;
import org.pgpainless.exception.SignatureValidationException;
import org.pgpainless.implementation.ImplementationFactory;
import org.pgpainless.key.OpenPgpFingerprint;
import org.pgpainless.policy.Policy;
import org.pgpainless.signature.SignatureUtils;
import org.pgpainless.signature.subpackets.SignatureSubpacketsUtil;
import org.pgpainless.util.DateUtil;
import org.pgpainless.util.NotationRegistry;
/**
* A collection of validators that perform validation steps over signatures.
*/
public abstract class SignatureValidator {
public abstract void verify(PGPSignature signature) throws SignatureValidationException;
/**
* Check, whether there is the possibility that the given signature was created by the given key.
* {@link #verify(PGPSignature)} throws a {@link SignatureValidationException} if we can say with certainty that
* the signature was not created by the given key (e.g. if the sig carries another issuer, issuer fingerprint packet).
*
* If there is no information found in the signature about who created it (no issuer, no fingerprint),
* {@link #verify(PGPSignature)} will simply return since it is plausible that the given key created the sig.
*
* @param signingKey signing key
* @return validator that throws a {@link SignatureValidationException} if the signature was not possibly made by
* the given key.
*/
public static SignatureValidator wasPossiblyMadeByKey(PGPPublicKey signingKey) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
OpenPgpFingerprint signingKeyFingerprint = OpenPgpFingerprint.of(signingKey);
Long issuer = SignatureSubpacketsUtil.getIssuerKeyIdAsLong(signature);
if (issuer != null) {
if (issuer != signingKey.getKeyID()) {
throw new SignatureValidationException("Signature was not created by " +
signingKeyFingerprint + " (signature issuer: " + Long.toHexString(issuer) + ")");
}
}
OpenPgpFingerprint fingerprint =
SignatureSubpacketsUtil.getIssuerFingerprintAsOpenPgpFingerprint(signature);
if (fingerprint != null) {
if (!fingerprint.equals(signingKeyFingerprint)) {
throw new SignatureValidationException("Signature was not created by " +
signingKeyFingerprint + " (signature fingerprint: " + fingerprint + ")");
}
}
// No issuer information found, so we cannot rule out that we did not create the sig
}
};
}
/**
* Verify that a subkey binding signature - if the subkey is signing-capable - contains a valid primary key
* binding signature.
*
* @param primaryKey primary key
* @param subkey subkey
* @param policy policy
* @param referenceDate reference date for signature verification
* @return validator
*/
public static SignatureValidator hasValidPrimaryKeyBindingSignatureIfRequired(PGPPublicKey primaryKey,
PGPPublicKey subkey, Policy policy,
Date referenceDate) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
if (!PublicKeyAlgorithm.requireFromId(signature.getKeyAlgorithm()).isSigningCapable()) {
// subkey is not signing capable -> No need to process embedded sigs
return;
}
KeyFlags keyFlags = SignatureSubpacketsUtil.getKeyFlags(signature);
if (keyFlags == null) {
return;
}
if (!KeyFlag.hasKeyFlag(keyFlags.getFlags(), KeyFlag.SIGN_DATA)
&& !KeyFlag.hasKeyFlag(keyFlags.getFlags(), KeyFlag.CERTIFY_OTHER)) {
return;
}
try {
PGPSignatureList embeddedSignatures = SignatureSubpacketsUtil.getEmbeddedSignature(signature);
if (embeddedSignatures == null) {
throw new SignatureValidationException(
"Missing primary key binding signature on signing capable subkey " +
Long.toHexString(subkey.getKeyID()), Collections.emptyMap());
}
boolean hasValidPrimaryKeyBinding = false;
Map<PGPSignature, Exception> rejectedEmbeddedSigs = new ConcurrentHashMap<>();
for (PGPSignature embedded : embeddedSignatures) {
if (SignatureType.valueOf(embedded.getSignatureType()) == SignatureType.PRIMARYKEY_BINDING) {
try {
signatureStructureIsAcceptable(subkey, policy).verify(embedded);
signatureIsEffective(referenceDate).verify(embedded);
correctPrimaryKeyBindingSignature(primaryKey, subkey).verify(embedded);
hasValidPrimaryKeyBinding = true;
break;
} catch (SignatureValidationException e) {
rejectedEmbeddedSigs.put(embedded, e);
}
}
}
if (!hasValidPrimaryKeyBinding) {
throw new SignatureValidationException(
"Missing primary key binding signature on signing capable subkey " +
Long.toHexString(subkey.getKeyID()), rejectedEmbeddedSigs);
}
} catch (PGPException e) {
throw new SignatureValidationException("Cannot process list of embedded signatures.", e);
}
}
};
}
/**
* Verify that a signature has an acceptable structure.
*
* @param signingKey signing key
* @param policy policy
* @return validator
*/
public static SignatureValidator signatureStructureIsAcceptable(PGPPublicKey signingKey, Policy policy) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
signatureIsNotMalformed(signingKey).verify(signature);
if (signature.getVersion() >= 4) {
signatureDoesNotHaveCriticalUnknownNotations(policy.getNotationRegistry()).verify(signature);
signatureDoesNotHaveCriticalUnknownSubpackets().verify(signature);
}
signatureUsesAcceptableHashAlgorithm(policy).verify(signature);
signatureUsesAcceptablePublicKeyAlgorithm(policy, signingKey).verify(signature);
}
};
}
/**
* Verify that a signature was made using an acceptable {@link PublicKeyAlgorithm}.
*
* @param policy policy
* @param signingKey signing key
* @return validator
*/
public static SignatureValidator signatureUsesAcceptablePublicKeyAlgorithm(Policy policy,
PGPPublicKey signingKey) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
PublicKeyAlgorithm algorithm = PublicKeyAlgorithm.requireFromId(signingKey.getAlgorithm());
int bitStrength = signingKey.getBitStrength();
if (bitStrength == -1) {
throw new SignatureValidationException("Cannot determine bit strength of signing key.");
}
if (!policy.getPublicKeyAlgorithmPolicy().isAcceptable(algorithm, bitStrength)) {
throw new SignatureValidationException("Signature was made using unacceptable key. " +
algorithm + " (" + bitStrength +
" bits) is not acceptable according to the public key algorithm policy.");
}
}
};
}
/**
* Verify that a signature uses an acceptable {@link HashAlgorithm}.
*
* @param policy policy
* @return validator
*/
public static SignatureValidator signatureUsesAcceptableHashAlgorithm(Policy policy) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
try {
HashAlgorithm hashAlgorithm = HashAlgorithm.requireFromId(signature.getHashAlgorithm());
Policy.HashAlgorithmPolicy hashAlgorithmPolicy =
getHashAlgorithmPolicyForSignature(signature, policy);
if (!hashAlgorithmPolicy.isAcceptable(signature.getHashAlgorithm(), signature.getCreationTime())) {
throw new SignatureValidationException("Signature uses unacceptable hash algorithm " +
hashAlgorithm + " (Signature creation time: " +
DateUtil.formatUTCDate(signature.getCreationTime()) + ")");
}
} catch (NoSuchElementException e) {
throw new SignatureValidationException("Signature uses unknown hash algorithm " +
signature.getHashAlgorithm());
}
}
};
}
/**
* Return the applicable {@link Policy.HashAlgorithmPolicy} for the given {@link PGPSignature}.
* Revocation signatures are being policed using a different policy than non-revocation signatures.
*
* @param signature signature
* @param policy revocation policy for revocation sigs, normal policy for non-rev sigs
* @return policy
*/
private static Policy.HashAlgorithmPolicy getHashAlgorithmPolicyForSignature(PGPSignature signature,
Policy policy) {
SignatureType type = SignatureType.valueOf(signature.getSignatureType());
Policy.HashAlgorithmPolicy hashAlgorithmPolicy;
if (type == SignatureType.CERTIFICATION_REVOCATION || type == SignatureType.KEY_REVOCATION ||
type == SignatureType.SUBKEY_REVOCATION) {
hashAlgorithmPolicy = policy.getRevocationSignatureHashAlgorithmPolicy();
} else {
hashAlgorithmPolicy = policy.getSignatureHashAlgorithmPolicy();
}
return hashAlgorithmPolicy;
}
/**
* Verify that a signature does not carry critical unknown notations.
*
* @param registry notation registry of known notations
* @return validator
*/
public static SignatureValidator signatureDoesNotHaveCriticalUnknownNotations(NotationRegistry registry) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
List<NotationData> hashedNotations = SignatureSubpacketsUtil.getHashedNotationData(signature);
for (NotationData notation : hashedNotations) {
if (!notation.isCritical()) {
continue;
}
if (!registry.isKnownNotation(notation.getNotationName())) {
throw new SignatureValidationException("Signature contains unknown critical notation '" +
notation.getNotationName() + "' in its hashed area.");
}
}
}
};
}
/**
* Verify that a signature does not contain critical unknown subpackets.
*
* @return validator
*/
public static SignatureValidator signatureDoesNotHaveCriticalUnknownSubpackets() {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
PGPSignatureSubpacketVector hashedSubpackets = signature.getHashedSubPackets();
for (int criticalTag : hashedSubpackets.getCriticalTags()) {
try {
SignatureSubpacket.requireFromCode(criticalTag);
} catch (NoSuchElementException e) {
throw new SignatureValidationException(
"Signature contains unknown critical subpacket of type " +
Long.toHexString(criticalTag));
}
}
}
};
}
/**
* Verify that a signature is effective right now.
*
* @return validator
*/
public static SignatureValidator signatureIsEffective() {
return signatureIsEffective(new Date());
}
/**
* Verify that a signature is effective at the given reference date.
*
* @param referenceDate reference date for signature verification
* @return validator
*/
public static SignatureValidator signatureIsEffective(Date referenceDate) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
signatureIsAlreadyEffective(referenceDate).verify(signature);
signatureIsNotYetExpired(referenceDate).verify(signature);
}
};
}
/**
* Verify that a signature was created prior to the given reference date.
*
* @param referenceDate reference date for signature verification
* @return validator
*/
public static SignatureValidator signatureIsAlreadyEffective(Date referenceDate) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
Date signatureCreationTime = SignatureSubpacketsUtil.getSignatureCreationTime(signature).getTime();
// Hard revocations are always effective
if (SignatureUtils.isHardRevocation(signature)) {
return;
}
if (signatureCreationTime.after(referenceDate)) {
throw new SignatureValidationException("Signature was created at " + signatureCreationTime +
" and is therefore not yet valid at " + referenceDate);
}
}
};
}
/**
* Verify that a signature is not yet expired.
*
* @param referenceDate reference date for signature verification
* @return validator
*/
public static SignatureValidator signatureIsNotYetExpired(Date referenceDate) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
// Hard revocations do not expire
if (SignatureUtils.isHardRevocation(signature)) {
return;
}
Date signatureExpirationTime = SignatureSubpacketsUtil.getSignatureExpirationTimeAsDate(signature);
if (signatureExpirationTime != null && signatureExpirationTime.before(referenceDate)) {
throw new SignatureValidationException("Signature is already expired (expiration: " +
signatureExpirationTime + ", validation: " + referenceDate + ")");
}
}
};
}
/**
* Verify that a signature is not malformed.
* A signature is malformed if it has no hashed creation time subpacket,
* it predates the creation time of the signing key, or it predates the creation date
* of the signing key binding signature.
*
* @param creator signing key
* @return validator
*/
public static SignatureValidator signatureIsNotMalformed(PGPPublicKey creator) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
if (signature.getVersion() >= 4) {
signatureHasHashedCreationTime().verify(signature);
}
signatureDoesNotPredateSigningKey(creator).verify(signature);
if (signature.getSignatureType() != SignatureType.PRIMARYKEY_BINDING.getCode()) {
signatureDoesNotPredateSigningKeyBindingDate(creator).verify(signature);
}
}
};
}
public static SignatureValidator signatureDoesNotPredateSignee(PGPPublicKey signee) {
return signatureDoesNotPredateKeyCreation(signee);
}
/**
* Verify that a signature has a hashed creation time subpacket.
*
* @return validator
*/
public static SignatureValidator signatureHasHashedCreationTime() {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
SignatureCreationTime creationTime = SignatureSubpacketsUtil.getSignatureCreationTime(signature);
if (creationTime == null) {
throw new SignatureValidationException(
"Malformed signature. Signature has no signature creation time subpacket in its hashed area.");
}
}
};
}
/**
* Verify that a signature does not predate the creation time of the signing key.
*
* @param key signing key
* @return validator
*/
public static SignatureValidator signatureDoesNotPredateSigningKey(PGPPublicKey key) {
return signatureDoesNotPredateKeyCreation(key);
}
/**
* Verify that a signature does not predate the creation time of the given key.
*
* @param key key
* @return validator
*/
public static SignatureValidator signatureDoesNotPredateKeyCreation(PGPPublicKey key) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
Date keyCreationTime = key.getCreationTime();
Date signatureCreationTime = signature.getCreationTime();
if (keyCreationTime.after(signatureCreationTime)) {
throw new SignatureValidationException("Signature predates key (key creation: " +
keyCreationTime + ", signature creation: " + signatureCreationTime + ")");
}
}
};
}
/**
* Verify that a signature does not predate the binding date of the signing key.
*
* @param signingKey signing key
* @return validator
*/
public static SignatureValidator signatureDoesNotPredateSigningKeyBindingDate(PGPPublicKey signingKey) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
if (signingKey.isMasterKey()) {
return;
}
boolean predatesBindingSig = true;
Iterator<PGPSignature> bindingSignatures =
signingKey.getSignaturesOfType(SignatureType.SUBKEY_BINDING.getCode());
if (!bindingSignatures.hasNext()) {
throw new SignatureValidationException("Signing subkey does not have a subkey binding signature.");
}
while (bindingSignatures.hasNext()) {
PGPSignature bindingSig = bindingSignatures.next();
if (!bindingSig.getCreationTime().after(signature.getCreationTime())) {
predatesBindingSig = false;
}
}
if (predatesBindingSig) {
throw new SignatureValidationException(
"Signature was created before the signing key was bound to the key ring.");
}
}
};
}
/**
* Verify that a subkey binding signature is correct.
*
* @param primaryKey primary key
* @param subkey subkey
* @return validator
*/
public static SignatureValidator correctSubkeyBindingSignature(PGPPublicKey primaryKey, PGPPublicKey subkey) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
if (primaryKey.getKeyID() == subkey.getKeyID()) {
throw new SignatureValidationException("Primary key cannot be its own subkey.");
}
try {
signature.init(ImplementationFactory.getInstance()
.getPgpContentVerifierBuilderProvider(), primaryKey);
boolean valid = signature.verifyCertification(primaryKey, subkey);
if (!valid) {
throw new SignatureValidationException("Signature is not correct.");
}
} catch (PGPException | ClassCastException e) {
throw new SignatureValidationException("Cannot verify subkey binding signature correctness", e);
}
}
};
}
/**
* Verify that a primary key binding signature is correct.
*
* @param primaryKey primary key
* @param subkey subkey
* @return validator
*/
public static SignatureValidator correctPrimaryKeyBindingSignature(PGPPublicKey primaryKey, PGPPublicKey subkey) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
try {
signature.init(ImplementationFactory.getInstance().getPgpContentVerifierBuilderProvider(), subkey);
boolean valid = signature.verifyCertification(primaryKey, subkey);
if (!valid) {
throw new SignatureValidationException("Primary Key Binding Signature is not correct.");
}
} catch (PGPException | ClassCastException e) {
throw new SignatureValidationException(
"Cannot verify primary key binding signature correctness", e);
}
}
};
}
/**
* Verify that a direct-key signature is correct.
*
* @param signer signing key
* @param signee signed key
* @return validator
*/
public static SignatureValidator correctSignatureOverKey(PGPPublicKey signer, PGPPublicKey signee) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
try {
signature.init(ImplementationFactory.getInstance().getPgpContentVerifierBuilderProvider(), signer);
boolean valid;
if (signer.getKeyID() == signee.getKeyID() || signature.getSignatureType() == PGPSignature.DIRECT_KEY) {
valid = signature.verifyCertification(signee);
} else {
valid = signature.verifyCertification(signer, signee);
}
if (!valid) {
throw new SignatureValidationException("Signature is not correct.");
}
} catch (PGPException | ClassCastException e) {
throw new SignatureValidationException("Cannot verify direct-key signature correctness", e);
}
}
};
}
/**
* Verify that a signature is a certification signature.
*
* @return validator
*/
public static SignatureValidator signatureIsCertification() {
return signatureIsOfType(
SignatureType.POSITIVE_CERTIFICATION,
SignatureType.CASUAL_CERTIFICATION,
SignatureType.GENERIC_CERTIFICATION,
SignatureType.NO_CERTIFICATION);
}
/**
* Verify that a signature type equals one of the given {@link SignatureType SignatureTypes}.
*
* @param signatureTypes one or more signature types
* @return validator
*/
public static SignatureValidator signatureIsOfType(SignatureType... signatureTypes) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
SignatureType type = SignatureType.valueOf(signature.getSignatureType());
boolean valid = false;
for (SignatureType allowed : signatureTypes) {
if (type == allowed) {
valid = true;
break;
}
}
if (!valid) {
throw new SignatureValidationException("Signature is of type " + type + " while only " +
Arrays.toString(signatureTypes) + " are allowed here.");
}
}
};
}
/**
* Verify that a signature over a user-id is correct.
*
* @param userId user-id
* @param certifiedKey key carrying the user-id
* @param certifyingKey key that created the signature.
* @return validator
*/
public static SignatureValidator correctSignatureOverUserId(String userId, PGPPublicKey certifiedKey,
PGPPublicKey certifyingKey) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
try {
signature.init(ImplementationFactory.getInstance()
.getPgpContentVerifierBuilderProvider(), certifyingKey);
boolean valid = signature.verifyCertification(userId, certifiedKey);
if (!valid) {
throw new SignatureValidationException("Signature over user-id '" + userId +
"' is not correct.");
}
} catch (PGPException | ClassCastException e) {
throw new SignatureValidationException("Cannot verify signature over user-id '" +
userId + "'.", e);
}
}
};
}
/**
* Verify that a signature over a user-attribute packet is correct.
*
* @param userAttributes user attributes
* @param certifiedKey key carrying the user-attributes
* @param certifyingKey key that created the certification signature
* @return validator
*/
public static SignatureValidator correctSignatureOverUserAttributes(PGPUserAttributeSubpacketVector userAttributes,
PGPPublicKey certifiedKey,
PGPPublicKey certifyingKey) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
try {
signature.init(ImplementationFactory.getInstance()
.getPgpContentVerifierBuilderProvider(), certifyingKey);
boolean valid = signature.verifyCertification(userAttributes, certifiedKey);
if (!valid) {
throw new SignatureValidationException("Signature over user-attribute vector is not correct.");
}
} catch (PGPException | ClassCastException e) {
throw new SignatureValidationException("Cannot verify signature over user-attribute vector.", e);
}
}
};
}
public static SignatureValidator signatureWasCreatedInBounds(Date notBefore, Date notAfter) {
return new SignatureValidator() {
@Override
public void verify(PGPSignature signature) throws SignatureValidationException {
Date timestamp = signature.getCreationTime();
if (notBefore != null && timestamp.before(notBefore)) {
throw new SignatureValidationException(
"Signature was made before the earliest allowed signature creation time. Created: " +
DateUtil.formatUTCDate(timestamp) + " Earliest allowed: " +
DateUtil.formatUTCDate(notBefore));
}
if (notAfter != null && timestamp.after(notAfter)) {
throw new SignatureValidationException(
"Signature was made after the latest allowed signature creation time. Created: " +
DateUtil.formatUTCDate(timestamp) + " Latest allowed: " +
DateUtil.formatUTCDate(notAfter));
}
}
};
}
}

11
pgpainless-core/src/main/kotlin/org/bouncycastle/extensions/PGPSignatureExtensions.kt
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@ -8,6 +8,8 @@ import java.util.*
import openpgp.plusSeconds
import org.bouncycastle.openpgp.PGPPublicKey
import org.bouncycastle.openpgp.PGPSignature
import org.pgpainless.algorithm.HashAlgorithm
import org.pgpainless.algorithm.PublicKeyAlgorithm
import org.pgpainless.algorithm.RevocationState
import org.pgpainless.algorithm.SignatureType
import org.pgpainless.key.OpenPgpFingerprint
@ -94,3 +96,12 @@ fun PGPSignature?.toRevocationState() =
val PGPSignature.fingerprint: OpenPgpFingerprint?
get() = SignatureSubpacketsUtil.getIssuerFingerprintAsOpenPgpFingerprint(this)
val PGPSignature.publicKeyAlgorithm: PublicKeyAlgorithm
get() = PublicKeyAlgorithm.requireFromId(keyAlgorithm)
val PGPSignature.signatureHashAlgorithm: HashAlgorithm
get() = HashAlgorithm.requireFromId(hashAlgorithm)
fun PGPSignature.isOfType(type: SignatureType): Boolean =
SignatureType.requireFromCode(signatureType) == type

693
pgpainless-core/src/main/kotlin/org/pgpainless/signature/consumer/SignatureValidator.kt Normal file
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@ -0,0 +1,693 @@
// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
//
// SPDX-License-Identifier: Apache-2.0
package org.pgpainless.signature.consumer
import java.lang.Exception
import java.util.Date
import openpgp.formatUTC
import openpgp.openPgpKeyId
import org.bouncycastle.extensions.fingerprint
import org.bouncycastle.extensions.isHardRevocation
import org.bouncycastle.extensions.isOfType
import org.bouncycastle.extensions.publicKeyAlgorithm
import org.bouncycastle.extensions.signatureExpirationDate
import org.bouncycastle.extensions.signatureHashAlgorithm
import org.bouncycastle.openpgp.PGPException
import org.bouncycastle.openpgp.PGPPublicKey
import org.bouncycastle.openpgp.PGPSignature
import org.bouncycastle.openpgp.PGPUserAttributeSubpacketVector
import org.pgpainless.algorithm.KeyFlag
import org.pgpainless.algorithm.SignatureSubpacket
import org.pgpainless.algorithm.SignatureType
import org.pgpainless.exception.SignatureValidationException
import org.pgpainless.implementation.ImplementationFactory
import org.pgpainless.key.OpenPgpFingerprint
import org.pgpainless.policy.Policy
import org.pgpainless.signature.subpackets.SignatureSubpacketsUtil
import org.pgpainless.util.NotationRegistry
abstract class SignatureValidator {
@Throws(SignatureValidationException::class) abstract fun verify(signature: PGPSignature)
companion object {
/**
* Check, whether there is the possibility that the given signature was created by the given
* key. [verify] throws a [SignatureValidationException] if we can say with certainty that
* the signature was not created by the given key (e.g. if the sig carries another issuer,
* issuer fingerprint packet).
*
* If there is no information found in the signature about who created it (no issuer, no
* fingerprint), [verify] will simply return since it is plausible that the given key
* created the sig.
*
* @param signingKey signing key
* @return validator that throws a [SignatureValidationException] if the signature was not
* possibly made by the given key.
*/
@JvmStatic
fun wasPossiblyMadeByKey(signingKey: PGPPublicKey): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
val signingKeyFingerprint = OpenPgpFingerprint.of(signingKey)
val issuer = SignatureSubpacketsUtil.getIssuerKeyIdAsLong(signature)
if (issuer != null) {
if (issuer != signingKey.keyID) {
throw SignatureValidationException(
"Signature was not created by" +
" $signingKeyFingerprint (signature issuer: ${issuer.openPgpKeyId()})")
}
}
if (signature.fingerprint != null &&
signature.fingerprint != signingKeyFingerprint) {
throw SignatureValidationException(
"Signature was not created by" +
" $signingKeyFingerprint (signature fingerprint: ${signature.fingerprint})")
}
}
// No issuer information found, so we cannot rule out that we did not create the sig
}
}
/**
* Verify that a subkey binding signature - if the subkey is signing-capable - contains a
* valid primary key binding signature.
*
* @param primaryKey primary key
* @param subkey subkey
* @param policy policy
* @param referenceDate reference date for signature verification
* @return validator
*/
@JvmStatic
fun hasValidPrimaryKeyBindingSignatureIfRequired(
primaryKey: PGPPublicKey,
subkey: PGPPublicKey,
policy: Policy,
referenceTime: Date
): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
if (!signature.publicKeyAlgorithm.isSigningCapable()) {
// subkey is not signing capable -> No need to process embedded signatures
return
}
// Make sure we have key flags
SignatureSubpacketsUtil.getKeyFlags(signature)?.let {
if (!KeyFlag.hasKeyFlag(it.flags, KeyFlag.SIGN_DATA) &&
!KeyFlag.hasKeyFlag(it.flags, KeyFlag.CERTIFY_OTHER)) {
return
}
}
?: return
try {
val embeddedSignatures =
SignatureSubpacketsUtil.getEmbeddedSignature(signature)
if (embeddedSignatures.isEmpty) {
throw SignatureValidationException(
"Missing primary key binding" +
" signature on signing capable subkey ${subkey.keyID.openPgpKeyId()}",
mapOf())
}
val rejectedEmbeddedSignatures = mutableMapOf<PGPSignature, Exception>()
if (!embeddedSignatures.any { embedded ->
if (embedded.isOfType(SignatureType.PRIMARYKEY_BINDING)) {
try {
signatureStructureIsAcceptable(subkey, policy).verify(embedded)
signatureIsEffective(referenceTime).verify(embedded)
correctPrimaryKeyBindingSignature(primaryKey, subkey)
.verify(embedded)
return@any true
} catch (e: SignatureValidationException) {
rejectedEmbeddedSignatures[embedded] = e
}
}
false
}) {
throw SignatureValidationException(
"Missing primary key binding signature on signing capable subkey ${subkey.keyID.openPgpKeyId()}",
rejectedEmbeddedSignatures)
}
} catch (e: PGPException) {
throw SignatureValidationException(
"Cannot process list of embedded signatures.", e)
}
}
}
}
/**
* Verify that a signature has an acceptable structure.
*
* @param signingKey signing key
* @param policy policy
* @return validator
*/
@JvmStatic
fun signatureStructureIsAcceptable(
signingKey: PGPPublicKey,
policy: Policy
): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
signatureIsNotMalformed(signingKey).verify(signature)
if (signature.version >= 4) {
signatureDoesNotHaveCriticalUnknownNotations(policy.notationRegistry)
.verify(signature)
signatureDoesNotHaveCriticalUnknownSubpackets().verify(signature)
}
signatureUsesAcceptableHashAlgorithm(policy).verify(signature)
signatureUsesAcceptablePublicKeyAlgorithm(policy, signingKey).verify(signature)
}
}
}
/**
* Verify that a signature was made using an acceptable [PublicKeyAlgorithm].
*
* @param policy policy
* @param signingKey signing key
* @return validator
*/
@JvmStatic
fun signatureUsesAcceptablePublicKeyAlgorithm(
policy: Policy,
signingKey: PGPPublicKey
): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
if (signingKey.bitStrength == -1) {
throw SignatureValidationException(
"Cannot determine bit strength of signing key.")
}
if (!policy.publicKeyAlgorithmPolicy.isAcceptable(
signingKey.publicKeyAlgorithm, signingKey.bitStrength)) {
throw SignatureValidationException(
"Signature was made using unacceptable key. " +
"${signingKey.publicKeyAlgorithm} (${signingKey.bitStrength} bits) is " +
"not acceptable according to the public key algorithm policy.")
}
}
}
}
@JvmStatic
fun signatureUsesAcceptableHashAlgorithm(policy: Policy): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
try {
val algorithmPolicy = getHashAlgorithmPolicyForSignature(signature, policy)
if (!algorithmPolicy.isAcceptable(
signature.signatureHashAlgorithm, signature.creationTime)) {
throw SignatureValidationException(
"Signature uses unacceptable" +
" hash algorithm ${signature.signatureHashAlgorithm}" +
" (Signature creation time: ${signature.creationTime.formatUTC()})")
}
} catch (e: NoSuchElementException) {
throw SignatureValidationException(
"Signature uses unknown hash" + " algorithm ${signature.hashAlgorithm}")
}
}
}
}
/**
* Return the applicable [Policy.HashAlgorithmPolicy] for the given [PGPSignature].
* Revocation signatures are being policed using a different policy than non-revocation
* signatures.
*
* @param signature signature
* @param policy revocation policy for revocation sigs, normal policy for non-rev sigs
* @return policy
*/
@JvmStatic
private fun getHashAlgorithmPolicyForSignature(
signature: PGPSignature,
policy: Policy
): Policy.HashAlgorithmPolicy {
val type = SignatureType.requireFromCode(signature.signatureType)
return when (type) {
SignatureType.CERTIFICATION_REVOCATION,
SignatureType.KEY_REVOCATION,
SignatureType.SUBKEY_REVOCATION -> policy.revocationSignatureHashAlgorithmPolicy
else -> policy.signatureHashAlgorithmPolicy
}
}
/**
* Verify that a signature does not carry critical unknown notations.
*
* @param registry notation registry of known notations
* @return validator
*/
@JvmStatic
fun signatureDoesNotHaveCriticalUnknownNotations(
registry: NotationRegistry
): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
SignatureSubpacketsUtil.getHashedNotationData(signature)
.filter { it.isCritical && !registry.isKnownNotation(it.notationName) }
.forEach {
throw SignatureValidationException(
"Signature contains unknown critical notation '${it.notationName}' in its hashed area.")
}
}
}
}
/**
* Verify that a signature does not contain critical unknown subpackets.
*
* @return validator
*/
@JvmStatic
fun signatureDoesNotHaveCriticalUnknownSubpackets(): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
signature.hashedSubPackets.criticalTags.forEach {
try {
SignatureSubpacket.requireFromCode(it)
} catch (e: NoSuchElementException) {
throw SignatureValidationException(
"Signature contains unknown critical subpacket of type 0x${Integer.toHexString(it)}")
}
}
}
}
}
/**
* Verify that a signature is effective at the given reference date.
*
* @param referenceTime reference date for signature verification
* @return validator
*/
@JvmStatic
@JvmOverloads
fun signatureIsEffective(referenceTime: Date = Date()): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
signatureIsAlreadyEffective(referenceTime).verify(signature)
signatureIsNotYetExpired(referenceTime).verify(signature)
}
}
}
/**
* Verify that a signature was created prior to the given reference date.
*
* @param referenceTime reference date for signature verification
* @return validator
*/
@JvmStatic
fun signatureIsAlreadyEffective(referenceTime: Date): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
if (signature.isHardRevocation) {
return
}
if (signature.creationTime > referenceTime) {
throw SignatureValidationException(
"Signature was created at ${signature.creationTime.formatUTC()} and" +
" is therefore not yet valid at ${referenceTime.formatUTC()}")
}
}
}
}
/**
* Verify that a signature is not yet expired.
*
* @param referenceTime reference date for signature verification
* @return validator
*/
@JvmStatic
fun signatureIsNotYetExpired(referenceTime: Date): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
if (signature.isHardRevocation) {
return
}
val expirationDate = signature.signatureExpirationDate
if (expirationDate != null && expirationDate < referenceTime) {
throw SignatureValidationException(
"Signature is already expired " +
"(expiration: ${expirationDate.formatUTC()}," +
" validation: ${referenceTime.formatUTC()})")
}
}
}
}
/**
* Verify that a signature is not malformed. A signature is malformed if it has no hashed
* creation time subpacket, it predates the creation time of the signing key, or it predates
* the creation date of the signing key binding signature.
*
* @param signingKey signing key
* @return validator
*/
@JvmStatic
fun signatureIsNotMalformed(signingKey: PGPPublicKey): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
if (signature.version >= 4) {
signatureHasHashedCreationTime().verify(signature)
}
signatureDoesNotPredateSigningKey(signingKey).verify(signature)
if (!signature.isOfType(SignatureType.PRIMARYKEY_BINDING)) {
signatureDoesNotPredateSigningKeyBindingDate(signingKey).verify(signature)
}
}
}
}
@JvmStatic
fun signatureDoesNotPredateSignee(signee: PGPPublicKey): SignatureValidator {
return signatureDoesNotPredateKeyCreation(signee)
}
/**
* Verify that a signature does not predate the creation time of the signing key.
*
* @param key signing key
* @return validator
*/
@JvmStatic
fun signatureDoesNotPredateSigningKey(signingKey: PGPPublicKey): SignatureValidator {
return signatureDoesNotPredateKeyCreation(signingKey)
}
/**
* Verify that a signature does not predate the creation time of the given key.
*
* @param key key
* @return validator
*/
@JvmStatic
fun signatureDoesNotPredateKeyCreation(key: PGPPublicKey): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
if (key.creationTime > signature.creationTime) {
throw SignatureValidationException(
"Signature predates key" +
" (key creation: ${key.creationTime.formatUTC()}," +
" signature creation: ${signature.creationTime.formatUTC()})")
}
}
}
}
/**
* Verify that a signature has a hashed creation time subpacket.
*
* @return validator
*/
@JvmStatic
fun signatureHasHashedCreationTime(): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
if (SignatureSubpacketsUtil.getSignatureCreationTime(signature) == null) {
throw SignatureValidationException(
"Malformed signature." +
"Signature has no signature creation time subpacket in its hashed area.")
}
}
}
}
/**
* Verify that a signature does not predate the binding date of the signing key.
*
* @param signingKey signing key
* @return validator
*/
@JvmStatic
fun signatureDoesNotPredateSigningKeyBindingDate(
signingKey: PGPPublicKey
): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
if (signingKey.isMasterKey) {
return
}
if (signingKey
.getSignaturesOfType(SignatureType.SUBKEY_BINDING.code)
.asSequence()
.map {
if (signature.creationTime < it.creationTime) {
throw SignatureValidationException(
"Signature was created " +
"before the signing key was bound to the certificate.")
}
}
.none()) {
throw SignatureValidationException(
"Signing subkey does not have a subkey binding signature.")
}
}
}
}
/**
* Verify that a subkey binding signature is correct.
*
* @param primaryKey primary key
* @param subkey subkey
* @return validator
*/
@JvmStatic
fun correctSubkeyBindingSignature(
primaryKey: PGPPublicKey,
subkey: PGPPublicKey
): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
if (primaryKey.keyID == subkey.keyID) {
throw SignatureValidationException("Primary key cannot be its own subkey.")
}
try {
signature.init(
ImplementationFactory.getInstance().pgpContentVerifierBuilderProvider,
primaryKey)
if (!signature.verifyCertification(primaryKey, subkey)) {
throw SignatureValidationException("Signature is not correct.")
}
} catch (e: PGPException) {
throw SignatureValidationException(
"Cannot verify subkey binding signature correctness", e)
} catch (e: ClassCastException) {
throw SignatureValidationException(
"Cannot verify subkey binding signature correctness", e)
}
}
}
}
/**
* Verify that a primary key binding signature is correct.
*
* @param primaryKey primary key
* @param subkey subkey
* @return validator
*/
@JvmStatic
fun correctPrimaryKeyBindingSignature(
primaryKey: PGPPublicKey,
subkey: PGPPublicKey
): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
if (primaryKey.keyID == subkey.keyID) {
throw SignatureValidationException("Primary key cannot be its own subkey.")
}
try {
signature.init(
ImplementationFactory.getInstance().pgpContentVerifierBuilderProvider,
subkey)
if (!signature.verifyCertification(primaryKey, subkey)) {
throw SignatureValidationException(
"Primary Key Binding Signature is not correct.")
}
} catch (e: PGPException) {
throw SignatureValidationException(
"Cannot verify primary key binding signature correctness", e)
} catch (e: ClassCastException) {
throw SignatureValidationException(
"Cannot verify primary key binding signature correctness", e)
}
}
}
}
/**
* Verify that a direct-key signature is correct.
*
* @param signingKey signing key
* @param signedKey signed key
* @return validator
*/
@JvmStatic
fun correctSignatureOverKey(
signingKey: PGPPublicKey,
signedKey: PGPPublicKey
): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
try {
signature.init(
ImplementationFactory.getInstance().pgpContentVerifierBuilderProvider,
signingKey)
val valid =
if (signingKey.keyID == signedKey.keyID ||
signature.isOfType(SignatureType.DIRECT_KEY)) {
signature.verifyCertification(signedKey)
} else {
signature.verifyCertification(signingKey, signedKey)
}
if (!valid) {
throw SignatureValidationException("Signature is not correct.")
}
} catch (e: PGPException) {
throw SignatureValidationException(
"Cannot verify direct-key signature correctness", e)
} catch (e: ClassCastException) {
throw SignatureValidationException(
"Cannot verify direct-key signature correctness", e)
}
}
}
}
@JvmStatic
fun signatureIsCertification(): SignatureValidator {
return signatureIsOfType(
SignatureType.POSITIVE_CERTIFICATION,
SignatureType.CASUAL_CERTIFICATION,
SignatureType.GENERIC_CERTIFICATION,
SignatureType.NO_CERTIFICATION)
}
/**
* Verify that a signature type equals one of the given [SignatureType].
*
* @param signatureType one or more signature types
* @return validator
*/
@JvmStatic
fun signatureIsOfType(vararg signatureType: SignatureType): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
if (signatureType.none { signature.isOfType(it) }) {
throw SignatureValidationException(
"Signature is of type" +
" ${SignatureType.requireFromCode(signature.signatureType)}, " +
"while only ${signatureType.contentToString()} are allowed here.")
}
}
}
}
/**
* Verify that a signature over a user-id is correct.
*
* @param userId user-id
* @param certifiedKey key carrying the user-id
* @param certifyingKey key that created the signature.
* @return validator
*/
@JvmStatic
fun correctSignatureOverUserId(
userId: CharSequence,
certifiedKey: PGPPublicKey,
certifyingKey: PGPPublicKey
): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
try {
signature.init(
ImplementationFactory.getInstance().pgpContentVerifierBuilderProvider,
certifyingKey)
if (!signature.verifyCertification(userId.toString(), certifiedKey)) {
throw SignatureValidationException(
"Signature over user-id '$userId' is not valid.")
}
} catch (e: PGPException) {
throw SignatureValidationException(
"Cannot verify signature over user-id '$userId'.", e)
} catch (e: ClassCastException) {
throw SignatureValidationException(
"Cannot verify signature over user-id '$userId'.", e)
}
}
}
}
/**
* Verify that a signature over a user-attribute packet is correct.
*
* @param userAttributes user attributes
* @param certifiedKey key carrying the user-attributes
* @param certifyingKey key that created the certification signature
* @return validator
*/
@JvmStatic
fun correctSignatureOverUserAttributes(
userAttributes: PGPUserAttributeSubpacketVector,
certifiedKey: PGPPublicKey,
certifyingKey: PGPPublicKey
): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
try {
signature.init(
ImplementationFactory.getInstance().pgpContentVerifierBuilderProvider,
certifyingKey)
if (!signature.verifyCertification(userAttributes, certifiedKey)) {
throw SignatureValidationException(
"Signature over user-attributes is not correct.")
}
} catch (e: PGPException) {
throw SignatureValidationException(
"Cannot verify signature over user-attribute vector.", e)
} catch (e: ClassCastException) {
throw SignatureValidationException(
"Cannot verify signature over user-attribute vector.", e)
}
}
}
}
@JvmStatic
fun signatureWasCreatedInBounds(notBefore: Date?, notAfter: Date?): SignatureValidator {
return object : SignatureValidator() {
override fun verify(signature: PGPSignature) {
val timestamp = signature.creationTime
if (notBefore != null && timestamp < notBefore) {
throw SignatureValidationException(
"Signature was made before the earliest allowed signature creation time." +
" Created: ${timestamp.formatUTC()}," +
" earliest allowed: ${notBefore.formatUTC()}")
}
if (notAfter != null && timestamp > notAfter) {
throw SignatureValidationException(
"Signature was made before the latest allowed signature creation time." +
" Created: ${timestamp.formatUTC()}," +
" latest allowed: ${notAfter.formatUTC()}")
}
}
}
}
}
}