Implement data structures from X.680, X.501, X.509, and PKCS#10, with X.690 encoding / decoding support

The implementation took four days, and it is still a little bit rough. Updated version should arrive soon.

Signed-off-by: Yuuta Liang <yuutaw@students.cs.ubc.ca>

11 files changed, 1134 insertions, 0 deletions

diff --git a/src/main/model/pki/AlgorithmIdentifier.java b/src/main/model/pki/AlgorithmIdentifier.java
new file mode 100644
index 0000000..421aa5a
--- /dev/null
+++ b/src/main/model/pki/AlgorithmIdentifier.java
@@ -0,0 +1,105 @@
+package model.pki;
+
+import model.asn1.ASN1Object;
+import model.asn1.ObjectIdentifier;
+import model.asn1.Tag;
+import model.asn1.exceptions.ParseException;
+import model.asn1.parsing.BytesReader;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.stream.Stream;
+
+/**
+ * Implements the following:
+ * <pre>
+ *   AttributeTypeAndValue ::= SEQUENCE {
+ *       type ATTRIBUTE.&id({SupportedAttributes}),
+ *       value ATTRIBUTE.&Type({SupportedAttributes}{@type}) OPTIONAL,
+ *   ... }
+ * </pre>
+ */
+public class AlgorithmIdentifier extends ASN1Object {
+    /**
+     * The type of that attribute. For example, <pre>1.2.840.113549.1.1.11</pre> is sha256WithRSAEncryption.
+     */
+    private final ObjectIdentifier type;
+
+    /**
+     * Additional parameters for that algorithm. Optional, and could be ASN.1 NULL or Java null (absent).
+     * According to RFC8017$A.2, it should be NULL for a number of algorithms:
+     * <pre>
+     *     PKCS1Algorithms    ALGORITHM-IDENTIFIER ::= {
+     *        { OID rsaEncryption                PARAMETERS NULL } |
+     *        { OID md2WithRSAEncryption         PARAMETERS NULL } |
+     *        { OID md5WithRSAEncryption         PARAMETERS NULL } |
+     *        { OID sha1WithRSAEncryption        PARAMETERS NULL } |
+     *        { OID sha224WithRSAEncryption      PARAMETERS NULL } |
+     *        { OID sha256WithRSAEncryption      PARAMETERS NULL } |
+     *        { OID sha384WithRSAEncryption      PARAMETERS NULL } |
+     *        { OID sha512WithRSAEncryption      PARAMETERS NULL } |
+     *        { OID sha512-224WithRSAEncryption  PARAMETERS NULL } |
+     *        { OID sha512-256WithRSAEncryption  PARAMETERS NULL } |
+     *        { OID id-RSAES-OAEP   PARAMETERS RSAES-OAEP-params } |
+     *        PKCS1PSourceAlgorithms                               |
+     *        { OID id-RSASSA-PSS   PARAMETERS RSASSA-PSS-params },
+     *        ...  -- Allows for future expansion --
+     *    }
+     * </pre>
+     */
+    private final ASN1Object parameters;
+
+    /**
+     * EFFECT: Init the object with tag, parentTag, type, and parameters. For tag and parentTag, see {@link ASN1Object}.
+     * REQUIRES: The values must match the type. Type tag should be UNIVERSAL OID. Parameters nullable.
+     */
+    public AlgorithmIdentifier(Tag tag, Tag parentTag,
+                               ObjectIdentifier type, ASN1Object parameters) {
+        super(tag, parentTag);
+        this.type = type;
+        this.parameters = parameters;
+    }
+
+    /**
+     * EFFECTS: Parse input DER. Parameters are not checked against the type.
+     *   Throws {@link ASN1Object} if invalid:
+     *    - Any fields missing
+     *    - Any fields having an incorrect tag (as seen in the ASN.1 definition)
+     *    - Any fields with encoding instructions that violate implicit / explicit encoding rules
+     *    - Other issues found during parsing the object, like early EOF (see {@link ASN1Object})
+     * MODIFIES: this, encoded
+     */
+    public AlgorithmIdentifier(BytesReader encoded, boolean hasParentTag) throws ParseException {
+        super(encoded, hasParentTag);
+        int i = encoded.getIndex();
+        this.type = new ObjectIdentifier(encoded, false);
+        this.type.getTag().enforce(ObjectIdentifier.TAG);
+        i = encoded.getIndex() - i;
+
+        if (getLength() > i) {
+            this.parameters = ASN1Object.parse(encoded, false);
+        } else {
+            this.parameters = null;
+        }
+    }
+
+    /**
+     * EFFECTS: Encode the fields into DER, in the order.
+     */
+    @Override
+    public Byte[] encodeValueDER() {
+        return Stream.of(Arrays.asList(type.encodeDER()),
+                parameters == null ? Collections.<Byte>emptyList() : Arrays.asList(parameters.encodeDER()))
+                .flatMap(Collection::stream)
+                .toArray(Byte[]::new);
+    }
+
+    public ObjectIdentifier getType() {
+        return type;
+    }
+
+    public ASN1Object getParameters() {
+        return parameters;
+    }
+}
diff --git a/src/main/model/pki/SubjectPublicKeyInfo.java b/src/main/model/pki/SubjectPublicKeyInfo.java
new file mode 100644
index 0000000..ac72055
--- /dev/null
+++ b/src/main/model/pki/SubjectPublicKeyInfo.java
@@ -0,0 +1,83 @@
+package model.pki;
+
+import model.asn1.ASN1Object;
+import model.asn1.BitString;
+import model.asn1.Tag;
+import model.asn1.exceptions.ParseException;
+import model.asn1.parsing.BytesReader;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.stream.Stream;
+
+/**
+ * Represents the following ASN.1 structure:
+ * <pre>
+ *     SubjectPublicKeyInfo ::= SEQUENCE {
+ *          algorithm AlgorithmIdentifier{{SupportedAlgorithms}},
+ *          subjectPublicKey BIT STRING,
+ *     ... }
+ * </pre>
+ * It represents the public key of a subject, in a certificate.
+ */
+public class SubjectPublicKeyInfo extends ASN1Object {
+    /**
+     * The algorithm used.
+     */
+    private final AlgorithmIdentifier algorithm;
+
+    /**
+     * The public key.
+     */
+    private final BitString subjectPublicKey;
+
+    /**
+     * EFFECTS: Init with tags, algorithm, subjectPublicKey. For tags, see {@link ASN1Object}.
+     * REQUIRES: The public key should be a valid $algorithm key. Algorithm and publicKey should have default UNIVERSAL
+     * tags (SEQUENCE and BIT STRING).
+     */
+    public SubjectPublicKeyInfo(Tag tag, Tag parentTag,
+                                final AlgorithmIdentifier algorithm,
+                                final BitString subjectPublicKey) {
+        super(tag, parentTag);
+        this.algorithm = algorithm;
+        this.subjectPublicKey = subjectPublicKey;
+    }
+
+    /**
+     * EFFECTS: Parse input DER.
+     *   Throws {@link ASN1Object} if invalid:
+     *    - Any fields missing (info, algorithm, signature)
+     *    - Any fields having an incorrect tag (as seen in the ASN.1 definition)
+     *    - Any fields with encoding instructions that violate implicit / explicit encoding rules
+     *    - Other issues found during parsing the object, like early EOF (see {@link ASN1Object})
+     * MODIFIES: this, encoded
+     */
+    public SubjectPublicKeyInfo(BytesReader encoded, boolean hasParentTag) throws ParseException {
+        super(encoded, hasParentTag);
+        this.algorithm = new AlgorithmIdentifier(encoded, false);
+        this.algorithm.getTag().enforce(TAG_SEQUENCE);
+
+        this.subjectPublicKey = new BitString(encoded, false);
+        this.subjectPublicKey.getTag().enforce(BitString.TAG);
+    }
+
+    /**
+     * EFFECTS: Encode the fields into DER, in the order.
+     */
+    @Override
+    public Byte[] encodeValueDER() {
+        return Stream.of(Arrays.asList(algorithm.encodeDER()),
+                        Arrays.asList(subjectPublicKey.encodeDER()))
+                .flatMap(Collection::stream)
+                .toArray(Byte[]::new);
+    }
+
+    public AlgorithmIdentifier getAlgorithm() {
+        return algorithm;
+    }
+
+    public BitString getSubjectPublicKey() {
+        return subjectPublicKey;
+    }
+}
diff --git a/src/main/model/pki/cert/Certificate.java b/src/main/model/pki/cert/Certificate.java
new file mode 100644
index 0000000..4e6c291
--- /dev/null
+++ b/src/main/model/pki/cert/Certificate.java
@@ -0,0 +1,127 @@
+package model.pki.cert;
+
+import model.asn1.ASN1Object;
+import model.asn1.BitString;
+import model.asn1.Tag;
+import model.asn1.exceptions.ParseException;
+import model.asn1.parsing.BytesReader;
+import model.pki.AlgorithmIdentifier;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.stream.Stream;
+
+/**
+ * Represents an X.509 signed certificate.
+ * <pre>
+ *    Certificate ::= SIGNED{TBSCertificate}
+ *
+ *    ENCRYPTED{ToBeEnciphered} ::= BIT STRING (CONSTRAINED BY {
+ *      -- shall be the result of applying an encipherment procedure
+ *      -- to the BER-encoded octets of a value of -- ToBeEnciphered } )
+ *
+ *    HASH{ToBeHashed} ::= SEQUENCE {
+ *      algorithmIdentifier AlgorithmIdentifier{{SupportedAlgorithms}},
+ *      hashValue BIT STRING (CONSTRAINED BY {
+ *          -- shall be the result of applying a hashing procedure to the DER-encoded
+ *          -- octets of a value of -- ToBeHashed } ),
+ *    ... }
+ *
+ *    ENCRYPTED-HASH{ToBeSigned} ::= BIT STRING (CONSTRAINED BY {
+ *      -- shall be the result of applying a hashing procedure to the DER-encoded (see 6.2)
+ *      -- octets of a value of -- ToBeSigned -- and then applying an encipherment procedure
+ *      -- to those octets -- } )
+ *
+ *    SIGNATURE{ToBeSigned} ::= SEQUENCE {
+ *      algorithmIdentifier AlgorithmIdentifier{{SupportedAlgorithms}},
+ *      encrypted ENCRYPTED-HASH{ToBeSigned},
+ *     ... }
+ *
+ *    SIGNED{ToBeSigned} ::= SEQUENCE {
+ *      toBeSigned ToBeSigned,
+ *      COMPONENTS OF SIGNATURE{ToBeSigned},
+ *    ... }
+ * </pre>
+ *
+ * A certificate creates a binding between the proposed subject name and the public key. It is only valid once a trusted
+ * CA signs it. Relying parties only need to trust a single trust anchor (the Root CA), and all of its issued certs are
+ * trusted. This is done through the cert tree: each certificate contains the Issued By field, indicating the DN of the
+ * upper level, all the way until the root CA, which is hard-coded in relying parties.
+ */
+public class Certificate extends ASN1Object {
+    /**
+     * All info of that cert, excluding the signature.
+     * It will be signed, and the signature is in <pre>signature</pre>.
+     */
+    private final TbsCertificate certificate;
+
+    /**
+     * The algorithm used for <pre>signature</pre>.
+     */
+    private final AlgorithmIdentifier signatureAlgorithm;
+
+    /**
+     * The signature.
+     */
+    private final BitString signature;
+
+    /**
+     * EFFECTS: Initialize the object with the given tag and parentTag, and info, signatureAlgorithm, and signature.
+     * REQUIRES: The algorithm must match the signature. The fields must have correct tags as described in the class
+     * specification (SEQUENCE, SEQUENCE, BIT STRING).
+     */
+    public Certificate(Tag tag, Tag parentTag,
+                       final TbsCertificate certificate,
+                       final AlgorithmIdentifier signatureAlgorithm,
+                       final BitString signature) {
+        super(tag, parentTag);
+        this.certificate = certificate;
+        this.signatureAlgorithm = signatureAlgorithm;
+        this.signature = signature;
+    }
+
+    /**
+     * EFFECTS: Parse input DER, without verifying the signature.
+     *   Throws {@link ParseException} if the input is invalid:
+     *    - Any fields missing
+     *    - Any fields having an incorrect tag (as seen in the ASN.1 definition)
+     *    - Any fields with encoding instructions that violate implicit / explicit encoding rules
+     *    - Other issues found during parsing the object, like early EOF (see {@link ASN1Object})
+     * MODIFIES: this, encoded
+     */
+    public Certificate(BytesReader encoded, boolean hasParentTag) throws ParseException {
+        super(encoded, hasParentTag);
+        this.certificate = new TbsCertificate(encoded, false);
+        this.certificate.getTag().enforce(TAG_SEQUENCE);
+
+        this.signatureAlgorithm = new AlgorithmIdentifier(encoded, false);
+        this.signatureAlgorithm.getTag().enforce(TAG_SEQUENCE);
+
+        this.signature = new BitString(encoded, false);
+        this.signature.getTag().enforce(BitString.TAG);
+    }
+
+    /**
+     * EFFECT: Encode that sequence into an ordered array of bytes, following the class specification.
+     */
+    @Override
+    public Byte[] encodeValueDER() {
+        return Stream.of(Arrays.asList(certificate.encodeDER()),
+                Arrays.asList(signatureAlgorithm.encodeDER()),
+                Arrays.asList(signature.encodeDER()))
+                .flatMap(Collection::stream)
+                .toArray(Byte[]::new);
+    }
+
+    public TbsCertificate getCertificate() {
+        return certificate;
+    }
+
+    public AlgorithmIdentifier getSignatureAlgorithm() {
+        return signatureAlgorithm;
+    }
+
+    public BitString getSignature() {
+        return signature;
+    }
+}
diff --git a/src/main/model/pki/cert/Extension.java b/src/main/model/pki/cert/Extension.java
new file mode 100644
index 0000000..0c104a4
--- /dev/null
+++ b/src/main/model/pki/cert/Extension.java
@@ -0,0 +1,113 @@
+package model.pki.cert;
+
+import model.asn1.*;
+import model.asn1.exceptions.ParseException;
+import model.asn1.parsing.BytesReader;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.stream.Stream;
+
+/**
+ * A X.509v3 certificate extension entry.
+ * <pre>
+ *     Extension ::= SEQUENCE {
+ *      extnId EXTENSION.&id({ExtensionSet}),
+ *      critical BOOLEAN DEFAULT FALSE,
+ *      extnValue OCTET STRING
+ *          (CONTAINING EXTENSION.&ExtnType({ExtensionSet}{@extnId})
+ *              ENCODED BY der),
+ *     ... }
+ * </pre>
+ * Extensions only exist in v3 certificates. They allow the CA and the relying party to add additional verification
+ * stages to the certificate to constraint its use or to supply additional information. For example, the CA may put a
+ * CDP (CRL Distribution Point) into the extensions.
+ */
+public class Extension extends ASN1Object {
+    /**
+     * The ID of the type of that extension.
+     */
+    private final ObjectIdentifier extnId;
+
+    /**
+     * Marking an extension critical means that the relying-party
+     * must reject that certificate if the type is unrecognized.
+     * If the type is recognized but cannot be fully parsed, the
+     * behaviour is undefined.
+     * Marking an extension critical reduces compatibility.
+     */
+    private final Bool critical;
+
+    /**
+     * The DER-encoded ASN.1 content of that extension.
+     */
+    private final OctetString extnValue;
+
+    /**
+     * EFFECTS: Init with tags, extnId, critical, and extnValue. For tags, see {@link ASN1Object}.
+     * extnValue is not checked against extnId.
+     * REQUIRES: Tags of extnId, critical, extnValue should be OID, BOOLEAN, OCTET STRING. The value should be a DER
+     * bytes octet string. If critical is unspecified (which defaults to false), put null.
+     */
+    public Extension(Tag tag, Tag parentTag,
+                     final ObjectIdentifier extnId,
+                     final Bool critical,
+                     final OctetString extnValue) {
+        super(tag, parentTag);
+        this.extnId = extnId;
+        this.critical = critical;
+        this.extnValue = extnValue;
+    }
+
+    /**
+     * EFFECTS: Parse input DER.
+     *   Throws {@link ParseException} if the input is invalid:
+     *    - Any fields missing
+     *    - Any fields having an incorrect tag (as seen in the ASN.1 definition)
+     *    - Any fields with encoding instructions that violate implicit / explicit encoding rules
+     *    - Other issues found during parsing the object, like early EOF (see {@link ASN1Object})
+     *    Note that critical is optional, and if it does not exist, it will be left as null, and it should be treated as
+     *    false.
+     * MODIFIES: this, encoded
+     */
+    public Extension(BytesReader encoded, boolean hasParentType) throws ParseException {
+        super(encoded, hasParentType);
+        this.extnId = new ObjectIdentifier(encoded, false);
+        this.extnId.getTag().enforce(ObjectIdentifier.TAG);
+
+        if (encoded.detectTag(Bool.TAG)) {
+            critical = new Bool(encoded, false);
+        } else {
+            critical = null;
+        }
+
+        this.extnValue = new OctetString(encoded, false);
+        this.extnValue.getTag().enforce(OctetString.TAG);
+    }
+
+    /**
+     * EFFECTS: Encode the DER.
+     */
+    @Override
+    public Byte[] encodeValueDER() {
+        return Stream.of(Arrays.asList(extnId.encodeDER()),
+                critical == null ? Collections.<Byte>emptyList() :
+                        Arrays.asList(critical.encodeDER()),
+                Arrays.asList(extnValue.encodeDER()))
+                .flatMap(Collection::stream)
+                .toArray(Byte[]::new);
+    }
+
+    public ObjectIdentifier getExtnId() {
+        return extnId;
+    }
+
+    public Bool getCritical() {
+        return critical;
+    }
+
+    public OctetString getExtnValue() {
+        return extnValue;
+    }
+}
diff --git a/src/main/model/pki/cert/Extensions.java b/src/main/model/pki/cert/Extensions.java
new file mode 100644
index 0000000..780fa2c
--- /dev/null
+++ b/src/main/model/pki/cert/Extensions.java
@@ -0,0 +1,67 @@
+package model.pki.cert;
+
+import model.asn1.ASN1Object;
+import model.asn1.Encodable;
+import model.asn1.Tag;
+import model.asn1.exceptions.ParseException;
+import model.asn1.parsing.BytesReader;
+import model.x501.RelativeDistinguishedName;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Stream;
+
+/**
+ * Represents an X.509 certificate extensions list:
+ * <pre>
+ *     Extensions ::= SEQUENCE OF Extension
+ * </pre>
+ */
+public class Extensions extends ASN1Object {
+    private final Extension[] extensions;
+
+    /**
+     * EFFECT: Initialize with the given tags and extensions. For tag and parentTag, consult
+     * {@link ASN1Object}.
+     * REQUIRES: Extensions should have SEQUENCE tag.
+     */
+    public Extensions(Tag tag, Tag parentTag, Extension[] extensions) {
+        super(tag, parentTag);
+        this.extensions = extensions;
+    }
+
+    /**
+     * EFFECT: Parse the Name from input DER bytes. For details on parsing, refer to {@link ASN1Object}.
+     *   Throws {@link ParseException} for invalid input.
+     * MODIFIES: this, encoded
+     */
+    public Extensions(BytesReader encoded, boolean hasParentTag) throws ParseException {
+        super(encoded, hasParentTag);
+        final List<Extension> list = new ArrayList<>();
+        for (int i = 0; i < getLength();) {
+            int index = encoded.getIndex();
+            final Extension ext = new Extension(encoded, false);
+            ext.getTag().enforce(TAG_SEQUENCE);
+            list.add(ext);
+            index = encoded.getIndex() - index;
+            i += index;
+        }
+        this.extensions = list.toArray(new Extension[0]);
+    }
+
+    /**
+     * EFFECTS: Encode the SEQUENCE OF into DER, keep order. RDNs will be encoded one-by-one.
+     */
+    @Override
+    public Byte[] encodeValueDER() {
+        return Stream.of(extensions)
+                .map(Encodable::encodeDER)
+                .flatMap(Arrays::stream)
+                .toArray(Byte[]::new);
+    }
+
+    public Extension[] getExtensions() {
+        return extensions;
+    }
+}
diff --git a/src/main/model/pki/cert/TbsCertificate.java b/src/main/model/pki/cert/TbsCertificate.java
new file mode 100644
index 0000000..1175456
--- /dev/null
+++ b/src/main/model/pki/cert/TbsCertificate.java
@@ -0,0 +1,263 @@
+package model.pki.cert;
+
+import model.asn1.*;
+import model.asn1.exceptions.ParseException;
+import model.asn1.parsing.BytesReader;
+import model.pki.AlgorithmIdentifier;
+import model.pki.SubjectPublicKeyInfo;
+import model.x501.Name;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.stream.Stream;
+
+/**
+ * Represents a X.509 certificate
+ *
+ * <pre>
+ *  Certificate ::= SIGNED{TBSCertificate}
+ *  TBSCertificate ::= SEQUENCE {
+ *      version                 [0] Version DEFAULT v1,
+ *      serialNumber            CertificateSerialNumber,
+ *      signature               AlgorithmIdentifier{{SupportedAlgorithms}},
+ *      issuer                  Name,
+ *      validity                Validity,
+ *      subject                 Name,
+ *      subjectPublicKeyInfo    SubjectPublicKeyInfo,
+ *      issuerUniqueIdentifier  [1] IMPLICIT UniqueIdentifier OPTIONAL,
+ *      ...,
+ *      [[2: -- if present, version shall be v2 or v3
+ *      subjectUniqueIdentifier [2] IMPLICIT UniqueIdentifier OPTIONAL]],
+ *      [[3: -- if present, version shall be v2 or v3
+ *      extensions              [3] Extensions OPTIONAL]]
+ *      -- If present, version shall be v3]]
+ *  }
+ *
+ *  Version ::= INTEGER {v1(0), v2(1), v3(2)}
+ *  CertificateSerialNumber ::= INTEGER
+ *
+ *  uniqueIdentifier ATTRIBUTE ::= {
+ *      WITH SYNTAX UniqueIdentifier
+ *      EQUALITY MATCHING RULE bitStringMatch
+ *      LDAP-SYNTAX bitString.&id
+ *      LDAP-NAME {"x500UniqueIdentifier"}
+ *      ID id-at-uniqueIdentifier }
+ *  UniqueIdentifier ::= BIT STRING
+ * </pre>
+ *
+ * NOTE that subjectUniqueIdentifier and issuerUniqueIdentifier are not supported.
+ */
+public class TbsCertificate extends ASN1Object {
+    // Version ::= INTEGER {v1(0), v2(1), v3(2)}
+    public static final int VERSION_V1 = 0;
+    public static final int VERSION_V2 = 1;
+    public static final int VERSION_V3 = 2;
+
+    /**
+     * The X.509 cert version. subjectUniqueIdentifier is v2 only, and extensions is v3 only.
+     * <pre>
+     *   [0] Version DEFAULT v1
+     * </pre>
+     */
+    private final Int version;
+
+    /**
+     * The serial number of that certificate that is unique across the CA.
+     * <pre>
+     *     serialNumber CertificateSerialNumber
+     *     CertificateSerialNumber ::= INTEGER
+     * </pre>
+     */
+    private final Int serialNumber;
+
+    private final AlgorithmIdentifier signature;
+
+    /**
+     * The subject and issuer distinguished names.
+     * <pre>
+     *     issuer Name,
+     *     subject Name
+     * </pre>
+     */
+    private final Name issuer;
+
+    /**
+     * The validity period of that certificate.
+     * Validity ::= SEQUENCE { notBefore Time, notAfter Time, ... }
+     */
+    private final Validity validity;
+
+    /**
+     * See the comments on issuer.
+     */
+    private final Name subject;
+
+    private final SubjectPublicKeyInfo subjectPublicKeyInfo;
+
+    /**
+     * [3] Optional.
+     */
+    private final Extensions extensions;
+
+    /**
+     * EFFECTS: Init with the given parameters. For tag and parentTag, see {@link ASN1Object}.
+     * REQUIRES:
+     *  - Version must be V1, V2, or V3.
+     *  - {issuer,subject}UniqueIdentifier could be null.
+     *  - If {issuer,subject}UniqueIdentifier presents, version must be V2 or V3.
+     *  - Extensions could be null.
+     *  - If extensions presents, version must be V3.
+     *  - The signature should be valid.
+     *  - Field and Desired Tags:
+     *    version       CONTEXT SPECIFIC 0 (EXPLICIT), INTEGER, OPTIONAL DEFAULT v1
+     *    serialNumber  INTEGER
+     *    signature     SEQUENCE
+     *    issuer        SEQUENCE
+     *    validity      SEQUENCE
+     *    subject       SEQUENCE
+     *    subjectPublicKeyInfo  SEQUENCE
+     *    extensions    CONTEXT SPECIFIC 3 (EXPLICIT), SEQUENCE, OPTIONAL
+     */
+    public TbsCertificate(Tag tag, Tag parentTag,
+                          final Int version,
+                          final Int serialNumber,
+                          final AlgorithmIdentifier signature,
+                          final Name issuer,
+                          final Validity validity,
+                          final Name subject,
+                          final SubjectPublicKeyInfo subjectPublicKeyInfo,
+                          final Extensions extensions) {
+        super(tag, parentTag);
+        this.version = version;
+        this.serialNumber = serialNumber;
+        this.signature = signature;
+        this.issuer = issuer;
+        this.validity = validity;
+        this.subject = subject;
+        this.subjectPublicKeyInfo = subjectPublicKeyInfo;
+        this.extensions = extensions;
+    }
+
+    /**
+     * EFFECTS: Parse input DER.
+     *   Throws {@link ASN1Object} if invalid:
+     *    - Any fields missing
+     *    - Any fields having an incorrect parent / inner tag (as seen in the ASN.1 definition)
+     *    - Any fields with encoding instructions that violate implicit / explicit encoding rules
+     *    - extensions are specified, but the version is v1 or v2
+     *    - Other issues found during parsing the object, like early EOF (see {@link ASN1Object})
+     * MODIFIES: this, encoded
+     */
+    public TbsCertificate(BytesReader encoded, boolean hasParentTag) throws ParseException {
+        super(encoded, hasParentTag);
+        int i = encoded.getIndex();
+        if (encoded.detectTag(new Tag(TagClass.CONTEXT_SPECIFIC, true, 0))) {
+            this.version = new Int(encoded, true);
+        } else {
+            this.version = null;
+        }
+        this.serialNumber = new Int(encoded, false);
+        this.signature = new AlgorithmIdentifier(encoded, false);
+        this.issuer = new Name(encoded, false);
+        this.validity = new Validity(encoded, false);
+        this.subject = new Name(encoded, false);
+        this.subjectPublicKeyInfo = new SubjectPublicKeyInfo(encoded, false);
+        if (encoded.detectTag(new Tag(TagClass.CONTEXT_SPECIFIC, true, 3))) {
+            this.extensions = new Extensions(encoded, true);
+        } else {
+            // Enforce the extensions tag - nothing else should be here.
+            if (Integer.compareUnsigned(getLength(), (encoded.getIndex() - i)) != 0) {
+                new Tag(encoded).enforce(new Tag(TagClass.CONTEXT_SPECIFIC, true, 3));
+            }
+            this.extensions = null;
+        }
+        enforceInput();
+        enforceVersion();
+    }
+
+    /**
+     * EFFECTS: Throw {@link ParseException} if any field have illegal tags.
+     */
+    private void enforceInput() throws ParseException {
+        if (this.version != null) {
+            this.version.getTag().enforce(Int.TAG);
+            this.version.getParentTag().enforce(new Tag(TagClass.CONTEXT_SPECIFIC, true, 0));
+        }
+        this.serialNumber.getTag().enforce(Int.TAG);
+        this.signature.getTag().enforce(TAG_SEQUENCE);
+        this.issuer.getTag().enforce(TAG_SEQUENCE);
+        this.validity.getTag().enforce(TAG_SEQUENCE);
+        this.subject.getTag().enforce(TAG_SEQUENCE);
+        this.subjectPublicKeyInfo.getTag().enforce(TAG_SEQUENCE);
+        if (extensions != null) {
+            this.extensions.getTag().enforce(TAG_SEQUENCE);
+            this.extensions.getParentTag().enforce(new Tag(TagClass.CONTEXT_SPECIFIC, true, 3));
+        }
+    }
+
+    /**
+     * EFFECTS: Throw {@link ParseException} if the version is incorrect.
+     */
+    private void enforceVersion() throws ParseException {
+        if (version != null
+                && (version.getLong() != VERSION_V1
+                && version.getLong() != VERSION_V2
+                && version.getLong() != VERSION_V3)) {
+            throw new ParseException("Illegal certificate version: " + version.getLong());
+        }
+        if (extensions != null && (version == null || version.getLong() != VERSION_V3)) {
+            throw new ParseException("Extensions present. The version must be v3 or above.");
+        }
+    }
+
+    /**
+     * EFFECTS: Encode into ordered DER.
+     */
+    @Override
+    public Byte[] encodeValueDER() {
+        return Stream.of(version == null ? Collections.<Byte>emptyList() : Arrays.asList(version.encodeDER()),
+                        Arrays.asList(serialNumber.encodeDER()),
+                        Arrays.asList(signature.encodeDER()),
+                        Arrays.asList(issuer.encodeDER()),
+                        Arrays.asList(validity.encodeDER()),
+                        Arrays.asList(subject.encodeDER()),
+                        Arrays.asList(subjectPublicKeyInfo.encodeDER()),
+                        extensions == null ? Collections.<Byte>emptyList()
+                                : Arrays.asList(extensions.encodeDER()))
+                .flatMap(Collection::stream)
+                .toArray(Byte[]::new);
+    }
+
+    public Int getVersion() {
+        return version;
+    }
+
+    public Int getSerialNumber() {
+        return serialNumber;
+    }
+
+    public AlgorithmIdentifier getSignature() {
+        return signature;
+    }
+
+    public Name getIssuer() {
+        return issuer;
+    }
+
+    public Validity getValidity() {
+        return validity;
+    }
+
+    public Name getSubject() {
+        return subject;
+    }
+
+    public SubjectPublicKeyInfo getSubjectPublicKeyInfo() {
+        return subjectPublicKeyInfo;
+    }
+
+    public Extensions getExtensions() {
+        return extensions;
+    }
+}
diff --git a/src/main/model/pki/cert/Validity.java b/src/main/model/pki/cert/Validity.java
new file mode 100644
index 0000000..76279ed
--- /dev/null
+++ b/src/main/model/pki/cert/Validity.java
@@ -0,0 +1,95 @@
+package model.pki.cert;
+
+import model.asn1.*;
+import model.asn1.exceptions.ParseException;
+import model.asn1.parsing.BytesReader;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.stream.Stream;
+
+/**
+ * Represents the following ASN.1 structure:
+ * <pre>
+ *     Validity ::= SEQUENCE {
+ *         notBefore Time,
+ *         notAfter Time,
+ *         ...
+ *     }
+ *
+ *     Time ::= CHOICE {
+ *         utcTime UTCTime,
+ *         generalizedTime GeneralizedTime
+ *     }
+ * </pre>
+ * It describes the validity period of the certificate.
+ */
+public class Validity extends ASN1Object {
+    /**
+     * The certificate is not valid before that time.
+     */
+    private final ASN1Time notBefore;
+
+    /**
+     * The certificate is not valid after that time.
+     */
+    private final ASN1Time notAfter;
+
+    /**
+     * EFFECTS: Init with the given tag, parentTag, notBefore, and notAfter. For more info on tag and parentTag, see
+     * {@link ASN1Object}.
+     * REQUIRES: notBefore and notAfter are either UTCTime or GeneralizedTime.
+     */
+    public Validity(Tag tag, Tag parentTag,
+                    ASN1Time notBefore, ASN1Time notAfter) {
+        super(tag, parentTag);
+        this.notBefore = notBefore;
+        this.notAfter = notAfter;
+    }
+
+    /**
+     * EFFECTS: Parse input DER.
+     *   Throws {@link ASN1Object} if invalid:
+     *    - Any fields missing (info, algorithm, signature)
+     *    - Any fields having an incorrect tag (as seen in the ASN.1 definition)
+     *    - Any fields with encoding instructions that violate implicit / explicit encoding rules
+     *    - Other issues found during parsing the object, like early EOF (see {@link ASN1Object})
+     * MODIFIES: this, encoded
+     */
+    public Validity(BytesReader encoded, boolean hasParentTag) throws ParseException {
+        super(encoded, hasParentTag);
+        if (encoded.detectTag(GeneralizedTime.TAG)) {
+            this.notBefore = new GeneralizedTime(encoded, false);
+            this.notBefore.getTag().enforce(GeneralizedTime.TAG);
+        } else {
+            this.notBefore = new UtcTime(encoded, false);
+            this.notBefore.getTag().enforce(UtcTime.TAG);
+        }
+        if (encoded.detectTag(GeneralizedTime.TAG)) {
+            this.notAfter = new GeneralizedTime(encoded, false);
+            this.notAfter.getTag().enforce(GeneralizedTime.TAG);
+        } else {
+            this.notAfter = new UtcTime(encoded, false);
+            this.notAfter.getTag().enforce(UtcTime.TAG);
+        }
+    }
+
+    /**
+     * EFFECTS: Encode into ordered DER.
+     */
+    @Override
+    public Byte[] encodeValueDER() {
+        return Stream.of(Arrays.asList(notBefore.encodeDER()),
+                Arrays.asList(notAfter.encodeDER()))
+                .flatMap(Collection::stream)
+                .toArray(Byte[]::new);
+    }
+
+    public ASN1Time getNotBefore() {
+        return notBefore;
+    }
+
+    public ASN1Time getNotAfter() {
+        return notAfter;
+    }
+}
diff --git a/src/main/model/pki/crl/CertificateList.java b/src/main/model/pki/crl/CertificateList.java
new file mode 100644
index 0000000..5142101
--- /dev/null
+++ b/src/main/model/pki/crl/CertificateList.java
@@ -0,0 +1,76 @@
+package model.pki.crl;
+
+import model.asn1.ASN1Object;
+import model.asn1.BitString;
+import model.asn1.Tag;
+import model.asn1.exceptions.ParseException;
+import model.asn1.parsing.BytesReader;
+import model.pki.AlgorithmIdentifier;
+import model.pki.cert.TbsCertificate;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.stream.Stream;
+
+/**
+ * Represents a signed X.509 CRL.
+ * <pre>
+ *      CertificateList ::= SIGNED{CertificateListContent}
+ * </pre>
+ */
+public class CertificateList extends ASN1Object {
+    /**
+     * All info of that CRL, excluding the signature.
+     * It will be signed, and the signature is in <pre>signature</pre>.
+     */
+    private final CertificateListContent crl;
+
+    /**
+     * The algorithm used for <pre>signature</pre>.
+     */
+    private final AlgorithmIdentifier signatureAlgorithm;
+
+    /**
+     * The signature.
+     */
+    private final BitString signature;
+
+    /**
+     * EFFECTS: Initialize the object with the given tag and parentTag, and list, signatureAlgorithm, and signature.
+     * REQUIRES: The algorithm must match the signature. The fields must have correct tags as described in the class
+     * specification (SEQUENCE, SEQUENCE, BIT STRING).
+     */
+    public CertificateList(Tag tag, Tag parentTag,
+                           final CertificateListContent crl,
+                           final AlgorithmIdentifier signatureAlgorithm,
+                           final BitString signature) {
+        super(tag, parentTag);
+        this.crl = crl;
+        this.signatureAlgorithm = signatureAlgorithm;
+        this.signature = signature;
+    }
+
+    /**
+     * EFFECT: Encode that sequence into an ordered array of bytes, following the class specification.
+     */
+    @Override
+    public Byte[] encodeValueDER() {
+        return Stream.of(Arrays.asList(crl.encodeDER()),
+                Arrays.asList(signatureAlgorithm.encodeDER()),
+                Arrays.asList(signature.encodeDER()))
+                .flatMap(Collection::stream)
+                .toArray(Byte[]::new);
+    }
+
+    public CertificateListContent getCrl() {
+        return crl;
+    }
+
+    public AlgorithmIdentifier getSignatureAlgorithm() {
+        return signatureAlgorithm;
+    }
+
+    public BitString getSignature() {
+        return signature;
+    }
+}
diff --git a/src/main/model/pki/crl/CertificateListContent.java b/src/main/model/pki/crl/CertificateListContent.java
new file mode 100644
index 0000000..6f75d71
--- /dev/null
+++ b/src/main/model/pki/crl/CertificateListContent.java
@@ -0,0 +1,106 @@
+package model.pki.crl;
+
+import model.asn1.*;
+import model.pki.AlgorithmIdentifier;
+import model.x501.Name;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+/**
+ * Represents a CRL content:
+ *
+ * <pre>
+ *     CertificateListContent ::= SEQUENCE {
+ *      version Version OPTIONAL,
+ *      -- if present, version shall be v2
+ *      signature AlgorithmIdentifier{{SupportedAlgorithms}},
+ *      issuer Name,
+ *      thisUpdate Time,
+ *      nextUpdate Time OPTIONAL,
+ *      revokedCertificates SEQUENCE OF SEQUENCE {
+ *        serialNumber CertificateSerialNumber,
+ *        revocationDate Time,
+ *        crlEntryExtensions Extensions OPTIONAL,
+ *        ...} OPTIONAL,
+ *      ...,
+ *      ...,
+ *      crlExtensions [0] Extensions OPTIONAL }
+ * </pre>
+ *
+ * A CRL is a signed object published by the CA that revokes any certificates signed by this CA before their
+ * expiration. Relying-parties should check the CRL from corresponding CDPs to see if the certificate to check is
+ * already revoked.
+ * Because the CA will only generate CRLs, this object won't be parsed.
+ */
+public class CertificateListContent extends ASN1Object {
+    private final Int version = new Int(Int.TAG, null, 1);
+    private final Name issuer;
+    private final AlgorithmIdentifier signature;
+    private final ASN1Time thisUpdate;
+    private final ASN1Time nextUpdate;
+    private final RevokedCertificate[] revokedCertificates;
+
+    /**
+     * EFFECTS: Init with tags and the given parameters. Version is always set to 1.
+     * REQUIRES: except for nextUpdate, all other fields are non-null; items in revokedCerts should be SEQUENCE.
+     */
+    public CertificateListContent(Tag tag, Tag parentTag,
+                                  Name issuer,
+                                  AlgorithmIdentifier signature,
+                                  ASN1Time thisUpdate,
+                                  ASN1Time nextUpdate,
+                                  RevokedCertificate[] revokedCertificates) {
+        super(tag, parentTag);
+        this.issuer = issuer;
+        this.signature = signature;
+        this.thisUpdate = thisUpdate;
+        this.nextUpdate = nextUpdate;
+        this.revokedCertificates = revokedCertificates;
+    }
+
+    @Override
+    public Byte[] encodeValueDER() {
+        final List<Byte> itemsEncoded = Arrays.stream(revokedCertificates)
+                .map(Encodable::encodeDER)
+                .flatMap(Arrays::stream)
+                .collect(Collectors.toList());
+        return Stream.of(Arrays.asList(version.encodeDER()),
+                Arrays.asList(issuer.encodeDER()),
+                Arrays.asList(signature.encodeDER()),
+                Arrays.asList(thisUpdate.encodeDER()),
+                nextUpdate == null ? Collections.<Byte>emptyList() : Arrays.asList(nextUpdate.encodeDER()),
+                Arrays.asList(new Tag(TagClass.UNIVERSAL, true, 0x30).encodeDER()),
+                Arrays.asList(new ASN1Length(itemsEncoded.size()).encodeDER()), itemsEncoded)
+                .flatMap(Collection::stream)
+                .toArray(Byte[]::new);
+    }
+
+    public Int getVersion() {
+        return version;
+    }
+
+    public Name getIssuer() {
+        return issuer;
+    }
+
+    public AlgorithmIdentifier getSignature() {
+        return signature;
+    }
+
+    public ASN1Time getThisUpdate() {
+        return thisUpdate;
+    }
+
+    public ASN1Time getNextUpdate() {
+        return nextUpdate;
+    }
+
+    public RevokedCertificate[] getRevokedCertificates() {
+        return revokedCertificates;
+    }
+}
diff --git a/src/main/model/pki/crl/Reason.java b/src/main/model/pki/crl/Reason.java
new file mode 100644
index 0000000..e47609e
--- /dev/null
+++ b/src/main/model/pki/crl/Reason.java
@@ -0,0 +1,27 @@
+package model.pki.crl;
+
+/**
+ * Identify the reason for revocation.
+ */
+public enum Reason {
+    UNSPECIFIED(0),
+    KEY_COMPROMISE(1),
+    CA_COMPROMISE(2),
+    AFFILIATION_CHANGED(3),
+    SUPERSEDED(4),
+    CESSATION_OF_OPERATION(5);
+
+    private final int val;
+
+    /**
+     * EFFECTS: Init with the specific val.
+     * REQUIRES: 0 <= val <= 0xFF
+     */
+    Reason(int val) {
+        this.val = val;
+    }
+
+    public int getVal() {
+        return val;
+    }
+}
diff --git a/src/main/model/pki/crl/RevokedCertificate.java b/src/main/model/pki/crl/RevokedCertificate.java
new file mode 100644
index 0000000..457ecb8
--- /dev/null
+++ b/src/main/model/pki/crl/RevokedCertificate.java
@@ -0,0 +1,72 @@
+package model.pki.crl;
+
+import model.asn1.*;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.stream.Stream;
+
+/**
+ * Indicates the revocation status of a certificate, given its serial number, revocation date, and reason.
+ * <pre>
+ *     SEQUENCE {
+ *        serialNumber CertificateSerialNumber,
+ *        revocationDate Time,
+ *        crlEntryExtensions Extensions OPTIONAL,
+ *     ...}
+ * </pre>
+ */
+public class RevokedCertificate extends ASN1Object {
+    private final Int serialNumber;
+    private final ASN1Time revocationDate;
+    private final Reason reason;
+
+    /**
+     * EFFECT: Init with tags and parameters. See {@link ASN1Object} for tags.
+     * REQUIRES: revocationDate should be either UtcTime or GeneralTime.
+     */
+    public RevokedCertificate(Tag tag, Tag parentTag,
+                              Int serialNumber,
+                              ASN1Time revocationDate,
+                              Reason reason) {
+        super(tag, parentTag);
+        this.serialNumber = serialNumber;
+        this.revocationDate = revocationDate;
+        this.reason = reason;
+    }
+
+    @Override
+    public Byte[] encodeValueDER() {
+        final Byte[] r = new OctetString(OctetString.TAG,
+                        null,
+                        new Byte[]{ 0x0A, 0x01, (byte) reason.getVal() })
+                        .encodeDER();
+        final Byte[] oid = new ObjectIdentifier(ObjectIdentifier.TAG, null, ObjectIdentifier.OID_CRL_REASON)
+                .encodeDER();
+        final Byte[] seqExt = Stream.of(Arrays.asList(TAG_SEQUENCE.encodeDER()),
+        Arrays.asList(new ASN1Length(r.length + oid.length).encodeDER()),
+        Arrays.asList(oid),
+        Arrays.asList(r))
+                .flatMap(Collection::stream)
+                .toArray(Byte[]::new);
+        return Stream.of(Arrays.asList(serialNumber.encodeDER()),
+                Arrays.asList(revocationDate.encodeDER()),
+                Arrays.asList(TAG_SEQUENCE.encodeDER()),
+                Arrays.asList(new ASN1Length(seqExt.length).encodeDER()),
+                Arrays.asList(seqExt))
+                .flatMap(Collection::stream)
+                .toArray(Byte[]::new);
+    }
+
+    public Int getSerialNumber() {
+        return serialNumber;
+    }
+
+    public ASN1Time getRevocationDate() {
+        return revocationDate;
+    }
+
+    public Reason getReason() {
+        return reason;
+    }
+}