--- /dev/null
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cryptobyte
+
+import (
+ "encoding/asn1"
+ "fmt"
+ "math/big"
+ "reflect"
+ "time"
+)
+
+// This file contains ASN.1-related methods for String and Builder.
+
+// Tag represents an ASN.1 tag number and class (together also referred to as
+// identifier octets). Methods in this package only support the low-tag-number
+// form, i.e. a single identifier octet with bits 7-8 encoding the class and
+// bits 1-6 encoding the tag number.
+type Tag uint8
+
+// Contructed returns t with the context-specific class bit set.
+func (t Tag) ContextSpecific() Tag { return t | 0x80 }
+
+// Contructed returns t with the constructed class bit set.
+func (t Tag) Constructed() Tag { return t | 0x20 }
+
+// Builder
+
+// AddASN1Int64 appends a DER-encoded ASN.1 INTEGER.
+func (b *Builder) AddASN1Int64(v int64) {
+ b.addASN1Signed(asn1.TagInteger, v)
+}
+
+// AddASN1Enum appends a DER-encoded ASN.1 ENUMERATION.
+func (b *Builder) AddASN1Enum(v int64) {
+ b.addASN1Signed(asn1.TagEnum, v)
+}
+
+func (b *Builder) addASN1Signed(tag Tag, v int64) {
+ b.AddASN1(tag, func(c *Builder) {
+ length := 1
+ for i := v; i >= 0x80 || i < -0x80; i >>= 8 {
+ length++
+ }
+
+ for ; length > 0; length-- {
+ i := v >> uint((length-1)*8) & 0xff
+ c.AddUint8(uint8(i))
+ }
+ })
+}
+
+// AddASN1Uint64 appends a DER-encoded ASN.1 INTEGER.
+func (b *Builder) AddASN1Uint64(v uint64) {
+ b.AddASN1(asn1.TagInteger, func(c *Builder) {
+ length := 1
+ for i := v; i >= 0x80; i >>= 8 {
+ length++
+ }
+
+ for ; length > 0; length-- {
+ i := v >> uint((length-1)*8) & 0xff
+ c.AddUint8(uint8(i))
+ }
+ })
+}
+
+// AddASN1BigInt appends a DER-encoded ASN.1 INTEGER.
+func (b *Builder) AddASN1BigInt(n *big.Int) {
+ if b.err != nil {
+ return
+ }
+
+ b.AddASN1(asn1.TagInteger, func(c *Builder) {
+ if n.Sign() < 0 {
+ // A negative number has to be converted to two's-complement form. So we
+ // invert and subtract 1. If the most-significant-bit isn't set then
+ // we'll need to pad the beginning with 0xff in order to keep the number
+ // negative.
+ nMinus1 := new(big.Int).Neg(n)
+ nMinus1.Sub(nMinus1, bigOne)
+ bytes := nMinus1.Bytes()
+ for i := range bytes {
+ bytes[i] ^= 0xff
+ }
+ if bytes[0]&0x80 == 0 {
+ c.add(0xff)
+ }
+ c.add(bytes...)
+ } else if n.Sign() == 0 {
+ c.add(0)
+ } else {
+ bytes := n.Bytes()
+ if bytes[0]&0x80 != 0 {
+ c.add(0)
+ }
+ c.add(bytes...)
+ }
+ })
+}
+
+// AddASN1OctetString appends a DER-encoded ASN.1 OCTET STRING.
+func (b *Builder) AddASN1OctetString(bytes []byte) {
+ b.AddASN1(asn1.TagOctetString, func(c *Builder) {
+ c.AddBytes(bytes)
+ })
+}
+
+const generalizedTimeFormatStr = "20060102150405Z0700"
+
+// AddASN1GeneralizedTime appends a DER-encoded ASN.1 GENERALIZEDTIME.
+func (b *Builder) AddASN1GeneralizedTime(t time.Time) {
+ if t.Year() < 0 || t.Year() > 9999 {
+ b.err = fmt.Errorf("cryptobyte: cannot represent %v as a GeneralizedTime", t)
+ return
+ }
+ b.AddASN1(asn1.TagGeneralizedTime, func(c *Builder) {
+ c.AddBytes([]byte(t.Format(generalizedTimeFormatStr)))
+ })
+}
+
+// AddASN1BitString appends a DER-encoded ASN.1 BIT STRING.
+func (b *Builder) AddASN1BitString(s asn1.BitString) {
+ // TODO(martinkr): Implement.
+ b.MarshalASN1(s)
+}
+
+// MarshalASN1 calls asn1.Marshal on its input and appends the result if
+// successful or records an error if one occurred.
+func (b *Builder) MarshalASN1(v interface{}) {
+ // NOTE(martinkr): This is somewhat of a hack to allow propagation of
+ // asn1.Marshal errors into Builder.err. N.B. if you call MarshalASN1 with a
+ // value embedded into a struct, its tag information is lost.
+ if b.err != nil {
+ return
+ }
+ bytes, err := asn1.Marshal(v)
+ if err != nil {
+ b.err = err
+ return
+ }
+ b.AddBytes(bytes)
+}
+
+// AddASN1 appends an ASN.1 object. The object is prefixed with the given tag.
+// Tags greater than 30 are not supported and result in an error (i.e.
+// low-tag-number form only). The child builder passed to the
+// BuilderContinuation can be used to build the content of the ASN.1 object.
+func (b *Builder) AddASN1(tag Tag, f BuilderContinuation) {
+ if b.err != nil {
+ return
+ }
+ // Identifiers with the low five bits set indicate high-tag-number format
+ // (two or more octets), which we don't support.
+ if tag&0x1f == 0x1f {
+ b.err = fmt.Errorf("cryptobyte: high-tag number identifier octects not supported: 0x%x", tag)
+ return
+ }
+ b.AddUint8(uint8(tag))
+ b.addLengthPrefixed(1, true, f)
+}
+
+// String
+
+var bigIntType = reflect.TypeOf((*big.Int)(nil)).Elem()
+
+// ReadASN1Integer decodes an ASN.1 INTEGER into out and advances. If out does
+// not point to an integer or to a big.Int, it panics. It returns true on
+// success and false on error.
+func (s *String) ReadASN1Integer(out interface{}) bool {
+ if reflect.TypeOf(out).Kind() != reflect.Ptr {
+ panic("out is not a pointer")
+ }
+ switch reflect.ValueOf(out).Elem().Kind() {
+ case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+ var i int64
+ if !s.readASN1Int64(&i) || reflect.ValueOf(out).Elem().OverflowInt(i) {
+ return false
+ }
+ reflect.ValueOf(out).Elem().SetInt(i)
+ return true
+ case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+ var u uint64
+ if !s.readASN1Uint64(&u) || reflect.ValueOf(out).Elem().OverflowUint(u) {
+ return false
+ }
+ reflect.ValueOf(out).Elem().SetUint(u)
+ return true
+ case reflect.Struct:
+ if reflect.TypeOf(out).Elem() == bigIntType {
+ return s.readASN1BigInt(out.(*big.Int))
+ }
+ }
+ panic("out does not point to an integer type")
+}
+
+func checkASN1Integer(bytes []byte) bool {
+ if len(bytes) == 0 {
+ // An INTEGER is encoded with at least one octet.
+ return false
+ }
+ if len(bytes) == 1 {
+ return true
+ }
+ if bytes[0] == 0 && bytes[1]&0x80 == 0 || bytes[0] == 0xff && bytes[1]&0x80 == 0x80 {
+ // Value is not minimally encoded.
+ return false
+ }
+ return true
+}
+
+var bigOne = big.NewInt(1)
+
+func (s *String) readASN1BigInt(out *big.Int) bool {
+ var bytes String
+ if !s.ReadASN1(&bytes, asn1.TagInteger) || !checkASN1Integer(bytes) {
+ return false
+ }
+ if bytes[0]&0x80 == 0x80 {
+ // Negative number.
+ neg := make([]byte, len(bytes))
+ for i, b := range bytes {
+ neg[i] = ^b
+ }
+ out.SetBytes(neg)
+ out.Add(out, bigOne)
+ out.Neg(out)
+ } else {
+ out.SetBytes(bytes)
+ }
+ return true
+}
+
+func (s *String) readASN1Int64(out *int64) bool {
+ var bytes String
+ if !s.ReadASN1(&bytes, asn1.TagInteger) || !checkASN1Integer(bytes) || !asn1Signed(out, bytes) {
+ return false
+ }
+ return true
+}
+
+func asn1Signed(out *int64, n []byte) bool {
+ length := len(n)
+ if length > 8 {
+ return false
+ }
+ for i := 0; i < length; i++ {
+ *out <<= 8
+ *out |= int64(n[i])
+ }
+ // Shift up and down in order to sign extend the result.
+ *out <<= 64 - uint8(length)*8
+ *out >>= 64 - uint8(length)*8
+ return true
+}
+
+func (s *String) readASN1Uint64(out *uint64) bool {
+ var bytes String
+ if !s.ReadASN1(&bytes, asn1.TagInteger) || !checkASN1Integer(bytes) || !asn1Unsigned(out, bytes) {
+ return false
+ }
+ return true
+}
+
+func asn1Unsigned(out *uint64, n []byte) bool {
+ length := len(n)
+ if length > 9 || length == 9 && n[0] != 0 {
+ // Too large for uint64.
+ return false
+ }
+ if n[0]&0x80 != 0 {
+ // Negative number.
+ return false
+ }
+ for i := 0; i < length; i++ {
+ *out <<= 8
+ *out |= uint64(n[i])
+ }
+ return true
+}
+
+// ReadASN1Enum decodes an ASN.1 ENUMERATION into out and advances. It returns
+// true on success and false on error.
+func (s *String) ReadASN1Enum(out *int) bool {
+ var bytes String
+ var i int64
+ if !s.ReadASN1(&bytes, asn1.TagEnum) || !checkASN1Integer(bytes) || !asn1Signed(&i, bytes) {
+ return false
+ }
+ if int64(int(i)) != i {
+ return false
+ }
+ *out = int(i)
+ return true
+}
+
+func (s *String) readBase128Int(out *int) bool {
+ ret := 0
+ for i := 0; len(*s) > 0; i++ {
+ if i == 4 {
+ return false
+ }
+ ret <<= 7
+ b := s.read(1)[0]
+ ret |= int(b & 0x7f)
+ if b&0x80 == 0 {
+ *out = ret
+ return true
+ }
+ }
+ return false // truncated
+}
+
+// ReadASN1ObjectIdentifier decodes an ASN.1 OBJECT IDENTIFIER into out and
+// advances. It returns true on success and false on error.
+func (s *String) ReadASN1ObjectIdentifier(out *asn1.ObjectIdentifier) bool {
+ var bytes String
+ if !s.ReadASN1(&bytes, asn1.TagOID) || len(bytes) == 0 {
+ return false
+ }
+
+ // In the worst case, we get two elements from the first byte (which is
+ // encoded differently) and then every varint is a single byte long.
+ components := make([]int, len(bytes)+1)
+
+ // The first varint is 40*value1 + value2:
+ // According to this packing, value1 can take the values 0, 1 and 2 only.
+ // When value1 = 0 or value1 = 1, then value2 is <= 39. When value1 = 2,
+ // then there are no restrictions on value2.
+ var v int
+ if !bytes.readBase128Int(&v) {
+ return false
+ }
+ if v < 80 {
+ components[0] = v / 40
+ components[1] = v % 40
+ } else {
+ components[0] = 2
+ components[1] = v - 80
+ }
+
+ i := 2
+ for ; len(bytes) > 0; i++ {
+ if !bytes.readBase128Int(&v) {
+ return false
+ }
+ components[i] = v
+ }
+ *out = components[:i]
+ return true
+}
+
+// ReadASN1GeneralizedTime decodes an ASN.1 GENERALIZEDTIME into out and
+// advances. It returns true on success and false on error.
+func (s *String) ReadASN1GeneralizedTime(out *time.Time) bool {
+ var bytes String
+ if !s.ReadASN1(&bytes, asn1.TagGeneralizedTime) {
+ return false
+ }
+ t := string(bytes)
+ res, err := time.Parse(generalizedTimeFormatStr, t)
+ if err != nil {
+ return false
+ }
+ if serialized := res.Format(generalizedTimeFormatStr); serialized != t {
+ return false
+ }
+ *out = res
+ return true
+}
+
+// ReadASN1BitString decodes an ASN.1 BIT STRING into out and advances. It
+// returns true on success and false on error.
+func (s *String) ReadASN1BitString(out *asn1.BitString) bool {
+ var bytes String
+ if !s.ReadASN1(&bytes, asn1.TagBitString) || len(bytes) == 0 {
+ return false
+ }
+
+ paddingBits := uint8(bytes[0])
+ bytes = bytes[1:]
+ if paddingBits > 7 ||
+ len(bytes) == 0 && paddingBits != 0 ||
+ len(bytes) > 0 && bytes[len(bytes)-1]&(1<<paddingBits-1) != 0 {
+ return false
+ }
+
+ out.BitLength = len(bytes)*8 - int(paddingBits)
+ out.Bytes = bytes
+ return true
+}
+
+// ReadASN1Bytes reads the contents of a DER-encoded ASN.1 element (not including
+// tag and length bytes) into out, and advances. The element must match the
+// given tag. It returns true on success and false on error.
+func (s *String) ReadASN1Bytes(out *[]byte, tag Tag) bool {
+ return s.ReadASN1((*String)(out), tag)
+}
+
+// ReadASN1 reads the contents of a DER-encoded ASN.1 element (not including
+// tag and length bytes) into out, and advances. The element must match the
+// given tag. It returns true on success and false on error.
+//
+// Tags greater than 30 are not supported (i.e. low-tag-number format only).
+func (s *String) ReadASN1(out *String, tag Tag) bool {
+ var t Tag
+ if !s.ReadAnyASN1(out, &t) || t != tag {
+ return false
+ }
+ return true
+}
+
+// ReadASN1Element reads the contents of a DER-encoded ASN.1 element (including
+// tag and length bytes) into out, and advances. The element must match the
+// given tag. It returns true on success and false on error.
+//
+// Tags greater than 30 are not supported (i.e. low-tag-number format only).
+func (s *String) ReadASN1Element(out *String, tag Tag) bool {
+ var t Tag
+ if !s.ReadAnyASN1Element(out, &t) || t != tag {
+ return false
+ }
+ return true
+}
+
+// ReadAnyASN1 reads the contents of a DER-encoded ASN.1 element (not including
+// tag and length bytes) into out, sets outTag to its tag, and advances. It
+// returns true on success and false on error.
+//
+// Tags greater than 30 are not supported (i.e. low-tag-number format only).
+func (s *String) ReadAnyASN1(out *String, outTag *Tag) bool {
+ return s.readASN1(out, outTag, true /* skip header */)
+}
+
+// ReadAnyASN1Element reads the contents of a DER-encoded ASN.1 element
+// (including tag and length bytes) into out, sets outTag to is tag, and
+// advances. It returns true on success and false on error.
+//
+// Tags greater than 30 are not supported (i.e. low-tag-number format only).
+func (s *String) ReadAnyASN1Element(out *String, outTag *Tag) bool {
+ return s.readASN1(out, outTag, false /* include header */)
+}
+
+// PeekASN1Tag returns true if the next ASN.1 value on the string starts with
+// the given tag.
+func (s String) PeekASN1Tag(tag Tag) bool {
+ if len(s) == 0 {
+ return false
+ }
+ return Tag(s[0]) == tag
+}
+
+// ReadOptionalASN1 attempts to read the contents of a DER-encoded ASN.Element
+// (not including tag and length bytes) tagged with the given tag into out. It
+// stores whether an element with the tag was found in outPresent, unless
+// outPresent is nil. It returns true on success and false on error.
+func (s *String) ReadOptionalASN1(out *String, outPresent *bool, tag Tag) bool {
+ present := s.PeekASN1Tag(tag)
+ if outPresent != nil {
+ *outPresent = present
+ }
+ if present && !s.ReadASN1(out, tag) {
+ return false
+ }
+ return true
+}
+
+// ReadOptionalASN1Integer attempts to read an optional ASN.1 INTEGER
+// explicitly tagged with tag into out and advances. If no element with a
+// matching tag is present, it writes defaultValue into out instead. If out
+// does not point to an integer or to a big.Int, it panics. It returns true on
+// success and false on error.
+func (s *String) ReadOptionalASN1Integer(out interface{}, tag Tag, defaultValue interface{}) bool {
+ if reflect.TypeOf(out).Kind() != reflect.Ptr {
+ panic("out is not a pointer")
+ }
+ var present bool
+ var i String
+ if !s.ReadOptionalASN1(&i, &present, tag) {
+ return false
+ }
+ if !present {
+ switch reflect.ValueOf(out).Elem().Kind() {
+ case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
+ reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+ reflect.ValueOf(out).Elem().Set(reflect.ValueOf(defaultValue))
+ case reflect.Struct:
+ if reflect.TypeOf(out).Elem() != bigIntType {
+ panic("invalid integer type")
+ }
+ if reflect.TypeOf(defaultValue).Kind() != reflect.Ptr ||
+ reflect.TypeOf(defaultValue).Elem() != bigIntType {
+ panic("out points to big.Int, but defaultValue does not")
+ }
+ out.(*big.Int).Set(defaultValue.(*big.Int))
+ default:
+ panic("invalid integer type")
+ }
+ return true
+ }
+ if !i.ReadASN1Integer(out) || !i.Empty() {
+ return false
+ }
+ return true
+}
+
+// ReadOptionalASN1OctetString attempts to read an optional ASN.1 OCTET STRING
+// explicitly tagged with tag into out and advances. If no element with a
+// matching tag is present, it writes defaultValue into out instead. It returns
+// true on success and false on error.
+func (s *String) ReadOptionalASN1OctetString(out *[]byte, outPresent *bool, tag Tag) bool {
+ var present bool
+ var child String
+ if !s.ReadOptionalASN1(&child, &present, tag) {
+ return false
+ }
+ if outPresent != nil {
+ *outPresent = present
+ }
+ if present {
+ var oct String
+ if !child.ReadASN1(&oct, asn1.TagOctetString) || !child.Empty() {
+ return false
+ }
+ *out = oct
+ } else {
+ *out = nil
+ }
+ return true
+}
+
+func (s *String) readASN1(out *String, outTag *Tag, skipHeader bool) bool {
+ if len(*s) < 2 {
+ return false
+ }
+ tag, lenByte := (*s)[0], (*s)[1]
+
+ if tag&0x1f == 0x1f {
+ // ITU-T X.690 section 8.1.2
+ //
+ // An identifier octet with a tag part of 0x1f indicates a high-tag-number
+ // form identifier with two or more octets. We only support tags less than
+ // 31 (i.e. low-tag-number form, single octet identifier).
+ return false
+ }
+
+ if outTag != nil {
+ *outTag = Tag(tag)
+ }
+
+ // ITU-T X.690 section 8.1.3
+ //
+ // Bit 8 of the first length byte indicates whether the length is short- or
+ // long-form.
+ var length, headerLen uint32 // length includes headerLen
+ if lenByte&0x80 == 0 {
+ // Short-form length (section 8.1.3.4), encoded in bits 1-7.
+ length = uint32(lenByte) + 2
+ headerLen = 2
+ } else {
+ // Long-form length (section 8.1.3.5). Bits 1-7 encode the number of octets
+ // used to encode the length.
+ lenLen := lenByte & 0x7f
+ var len32 uint32
+
+ if lenLen == 0 || lenLen > 4 || len(*s) < int(2+lenLen) {
+ return false
+ }
+
+ lenBytes := String((*s)[2 : 2+lenLen])
+ if !lenBytes.readUnsigned(&len32, int(lenLen)) {
+ return false
+ }
+
+ // ITU-T X.690 section 10.1 (DER length forms) requires encoding the length
+ // with the minimum number of octets.
+ if len32 < 128 {
+ // Length should have used short-form encoding.
+ return false
+ }
+ if len32>>((lenLen-1)*8) == 0 {
+ // Leading octet is 0. Length should have been at least one byte shorter.
+ return false
+ }
+
+ headerLen = 2 + uint32(lenLen)
+ if headerLen+len32 < len32 {
+ // Overflow.
+ return false
+ }
+ length = headerLen + len32
+ }
+
+ if uint32(int(length)) != length || !s.ReadBytes((*[]byte)(out), int(length)) {
+ return false
+ }
+ if skipHeader && !out.Skip(int(headerLen)) {
+ panic("cryptobyte: internal error")
+ }
+
+ return true
+}
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