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/
signature-v4.go
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/
signature-v4.go
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/*
* Minio Cloud Storage, (C) 2015, 2016, 2017 Minio, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
// Package cmd This file implements helper functions to validate AWS
// Signature Version '4' authorization header.
//
// This package provides comprehensive helpers for following signature
// types.
// - Based on Authorization header.
// - Based on Query parameters.
// - Based on Form POST policy.
package cmd
import (
"bytes"
"crypto/subtle"
"encoding/hex"
"net/http"
"net/url"
"sort"
"strconv"
"strings"
"time"
"github.com/minio/minio-go/pkg/s3utils"
sha256 "github.com/minio/sha256-simd"
)
// AWS Signature Version '4' constants.
const (
signV4Algorithm = "AWS4-HMAC-SHA256"
iso8601Format = "20060102T150405Z"
yyyymmdd = "20060102"
)
// getCanonicalHeaders generate a list of request headers with their values
func getCanonicalHeaders(signedHeaders http.Header) string {
var headers []string
vals := make(http.Header)
for k, vv := range signedHeaders {
headers = append(headers, strings.ToLower(k))
vals[strings.ToLower(k)] = vv
}
sort.Strings(headers)
var buf bytes.Buffer
for _, k := range headers {
buf.WriteString(k)
buf.WriteByte(':')
for idx, v := range vals[k] {
if idx > 0 {
buf.WriteByte(',')
}
buf.WriteString(signV4TrimAll(v))
}
buf.WriteByte('\n')
}
return buf.String()
}
// getSignedHeaders generate a string i.e alphabetically sorted, semicolon-separated list of lowercase request header names
func getSignedHeaders(signedHeaders http.Header) string {
var headers []string
for k := range signedHeaders {
headers = append(headers, strings.ToLower(k))
}
sort.Strings(headers)
return strings.Join(headers, ";")
}
// getCanonicalRequest generate a canonical request of style
//
// canonicalRequest =
// <HTTPMethod>\n
// <CanonicalURI>\n
// <CanonicalQueryString>\n
// <CanonicalHeaders>\n
// <SignedHeaders>\n
// <HashedPayload>
//
func getCanonicalRequest(extractedSignedHeaders http.Header, payload, queryStr, urlPath, method string) string {
rawQuery := strings.Replace(queryStr, "+", "%20", -1)
encodedPath := s3utils.EncodePath(urlPath)
canonicalRequest := strings.Join([]string{
method,
encodedPath,
rawQuery,
getCanonicalHeaders(extractedSignedHeaders),
getSignedHeaders(extractedSignedHeaders),
payload,
}, "\n")
return canonicalRequest
}
// getScope generate a string of a specific date, an AWS region, and a service.
func getScope(t time.Time, region string) string {
scope := strings.Join([]string{
t.Format(yyyymmdd),
region,
"s3",
"aws4_request",
}, "/")
return scope
}
// getStringToSign a string based on selected query values.
func getStringToSign(canonicalRequest string, t time.Time, scope string) string {
stringToSign := signV4Algorithm + "\n" + t.Format(iso8601Format) + "\n"
stringToSign = stringToSign + scope + "\n"
canonicalRequestBytes := sha256.Sum256([]byte(canonicalRequest))
stringToSign = stringToSign + hex.EncodeToString(canonicalRequestBytes[:])
return stringToSign
}
// getSigningKey hmac seed to calculate final signature.
func getSigningKey(secretKey string, t time.Time, region string) []byte {
date := sumHMAC([]byte("AWS4"+secretKey), []byte(t.Format(yyyymmdd)))
regionBytes := sumHMAC(date, []byte(region))
service := sumHMAC(regionBytes, []byte("s3"))
signingKey := sumHMAC(service, []byte("aws4_request"))
return signingKey
}
// getSignature final signature in hexadecimal form.
func getSignature(signingKey []byte, stringToSign string) string {
return hex.EncodeToString(sumHMAC(signingKey, []byte(stringToSign)))
}
// Check to see if Policy is signed correctly.
func doesPolicySignatureMatch(formValues http.Header) APIErrorCode {
// For SignV2 - Signature field will be valid
if _, ok := formValues["Signature"]; ok {
return doesPolicySignatureV2Match(formValues)
}
return doesPolicySignatureV4Match(formValues)
}
// compareSignatureV4 returns true if and only if both signatures
// are equal. The signatures are expected to be HEX encoded strings
// according to the AWS S3 signature V4 spec.
func compareSignatureV4(sig1, sig2 string) bool {
// The CTC using []byte(str) works because the hex encoding
// is unique for a sequence of bytes. See also compareSignatureV2.
return subtle.ConstantTimeCompare([]byte(sig1), []byte(sig2)) == 1
}
// doesPolicySignatureMatch - Verify query headers with post policy
// - http://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-HTTPPOSTConstructPolicy.html
// returns ErrNone if the signature matches.
func doesPolicySignatureV4Match(formValues http.Header) APIErrorCode {
// Server region.
region := globalServerConfig.GetRegion()
// Parse credential tag.
credHeader, err := parseCredentialHeader("Credential="+formValues.Get("X-Amz-Credential"), region)
if err != ErrNone {
return ErrMissingFields
}
cred, _, s3Err := checkKeyValid(credHeader.accessKey)
if s3Err != ErrNone {
return s3Err
}
// Get signing key.
signingKey := getSigningKey(cred.SecretKey, credHeader.scope.date, credHeader.scope.region)
// Get signature.
newSignature := getSignature(signingKey, formValues.Get("Policy"))
// Verify signature.
if !compareSignatureV4(newSignature, formValues.Get("X-Amz-Signature")) {
return ErrSignatureDoesNotMatch
}
// Success.
return ErrNone
}
// doesPresignedSignatureMatch - Verify query headers with presigned signature
// - http://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-query-string-auth.html
// returns ErrNone if the signature matches.
func doesPresignedSignatureMatch(hashedPayload string, r *http.Request, region string) APIErrorCode {
// Copy request
req := *r
// Parse request query string.
pSignValues, err := parsePreSignV4(req.URL.Query(), region)
if err != ErrNone {
return err
}
cred, _, s3Err := checkKeyValid(pSignValues.Credential.accessKey)
if s3Err != ErrNone {
return s3Err
}
// Extract all the signed headers along with its values.
extractedSignedHeaders, errCode := extractSignedHeaders(pSignValues.SignedHeaders, r)
if errCode != ErrNone {
return errCode
}
// Construct new query.
query := make(url.Values)
if req.URL.Query().Get("X-Amz-Content-Sha256") != "" {
query.Set("X-Amz-Content-Sha256", hashedPayload)
}
query.Set("X-Amz-Algorithm", signV4Algorithm)
// If the host which signed the request is slightly ahead in time (by less than globalMaxSkewTime) the
// request should still be allowed.
if pSignValues.Date.After(UTCNow().Add(globalMaxSkewTime)) {
return ErrRequestNotReadyYet
}
if UTCNow().Sub(pSignValues.Date) > pSignValues.Expires {
return ErrExpiredPresignRequest
}
// Save the date and expires.
t := pSignValues.Date
expireSeconds := int(pSignValues.Expires / time.Second)
// Construct the query.
query.Set("X-Amz-Date", t.Format(iso8601Format))
query.Set("X-Amz-Expires", strconv.Itoa(expireSeconds))
query.Set("X-Amz-SignedHeaders", getSignedHeaders(extractedSignedHeaders))
query.Set("X-Amz-Credential", cred.AccessKey+"/"+getScope(t, pSignValues.Credential.scope.region))
// Save other headers available in the request parameters.
for k, v := range req.URL.Query() {
// Handle the metadata in presigned put query string
if strings.Contains(strings.ToLower(k), "x-amz-meta-") {
query.Set(k, v[0])
}
if strings.HasPrefix(strings.ToLower(k), "x-amz") {
continue
}
query[k] = v
}
// Get the encoded query.
encodedQuery := query.Encode()
// Verify if date query is same.
if req.URL.Query().Get("X-Amz-Date") != query.Get("X-Amz-Date") {
return ErrSignatureDoesNotMatch
}
// Verify if expires query is same.
if req.URL.Query().Get("X-Amz-Expires") != query.Get("X-Amz-Expires") {
return ErrSignatureDoesNotMatch
}
// Verify if signed headers query is same.
if req.URL.Query().Get("X-Amz-SignedHeaders") != query.Get("X-Amz-SignedHeaders") {
return ErrSignatureDoesNotMatch
}
// Verify if credential query is same.
if req.URL.Query().Get("X-Amz-Credential") != query.Get("X-Amz-Credential") {
return ErrSignatureDoesNotMatch
}
// Verify if sha256 payload query is same.
if req.URL.Query().Get("X-Amz-Content-Sha256") != "" {
if req.URL.Query().Get("X-Amz-Content-Sha256") != query.Get("X-Amz-Content-Sha256") {
return ErrContentSHA256Mismatch
}
}
/// Verify finally if signature is same.
// Get canonical request.
presignedCanonicalReq := getCanonicalRequest(extractedSignedHeaders, hashedPayload, encodedQuery, req.URL.Path, req.Method)
// Get string to sign from canonical request.
presignedStringToSign := getStringToSign(presignedCanonicalReq, t, pSignValues.Credential.getScope())
// Get hmac presigned signing key.
presignedSigningKey := getSigningKey(cred.SecretKey, pSignValues.Credential.scope.date, pSignValues.Credential.scope.region)
// Get new signature.
newSignature := getSignature(presignedSigningKey, presignedStringToSign)
// Verify signature.
if !compareSignatureV4(req.URL.Query().Get("X-Amz-Signature"), newSignature) {
return ErrSignatureDoesNotMatch
}
return ErrNone
}
// doesSignatureMatch - Verify authorization header with calculated header in accordance with
// - http://docs.aws.amazon.com/AmazonS3/latest/API/sig-v4-authenticating-requests.html
// returns ErrNone if signature matches.
func doesSignatureMatch(hashedPayload string, r *http.Request, region string) APIErrorCode {
// Copy request.
req := *r
// Save authorization header.
v4Auth := req.Header.Get("Authorization")
// Parse signature version '4' header.
signV4Values, err := parseSignV4(v4Auth, region)
if err != ErrNone {
return err
}
// Extract all the signed headers along with its values.
extractedSignedHeaders, errCode := extractSignedHeaders(signV4Values.SignedHeaders, r)
if errCode != ErrNone {
return errCode
}
cred, _, s3Err := checkKeyValid(signV4Values.Credential.accessKey)
if s3Err != ErrNone {
return s3Err
}
// Extract date, if not present throw error.
var date string
if date = req.Header.Get(http.CanonicalHeaderKey("x-amz-date")); date == "" {
if date = r.Header.Get("Date"); date == "" {
return ErrMissingDateHeader
}
}
// Parse date header.
t, e := time.Parse(iso8601Format, date)
if e != nil {
return ErrMalformedDate
}
// Query string.
queryStr := req.URL.Query().Encode()
// Get canonical request.
canonicalRequest := getCanonicalRequest(extractedSignedHeaders, hashedPayload, queryStr, req.URL.Path, req.Method)
// Get string to sign from canonical request.
stringToSign := getStringToSign(canonicalRequest, t, signV4Values.Credential.getScope())
// Get hmac signing key.
signingKey := getSigningKey(cred.SecretKey, signV4Values.Credential.scope.date, signV4Values.Credential.scope.region)
// Calculate signature.
newSignature := getSignature(signingKey, stringToSign)
// Verify if signature match.
if !compareSignatureV4(newSignature, signV4Values.Signature) {
return ErrSignatureDoesNotMatch
}
// Return error none.
return ErrNone
}