Tags: Amazon Web Services (AWS) , Security

Complete implementation of Amazon Web Service version 4 signing process in Java. Each step of
http://docs.aws.amazon.com/general/latest/gr/sigv4_signing.html is described in code.

Source code (AWSV4Auth.java)
It will calculate signature based on given data and return the headers. This code works fine with Amazon Elasticsearch Service. If you are working around another Amazon Web Service then you might need to change few lines of code but mostly it'll work.

import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;
import java.util.TimeZone;
import java.util.TreeMap;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

/**
 * Example: Signing AWS Requests with Signature Version 4 in Java.
 *
 * @reference: http://docs.aws.amazon.com/general/latest/gr/sigv4_signing.html
 * @author javaQuery
 * @date 19th January, 2016
 * @Github: https://github.com/javaquery/Examples
 */
public class AWSV4Auth {

    private AWSV4Auth() {
    }

    public static class Builder {

        private String accessKeyID;
        private String secretAccessKey;
        private String regionName;
        private String serviceName;
        private String httpMethodName;
        private String canonicalURI;
        private TreeMap<String, String> queryParametes;
        private TreeMap<String, String> awsHeaders;
        private String payload;
        private boolean debug = false;

        public Builder(String accessKeyID, String secretAccessKey) {
            this.accessKeyID = accessKeyID;
            this.secretAccessKey = secretAccessKey;
        }

        public Builder regionName(String regionName) {
            this.regionName = regionName;
            return this;
        }

        public Builder serviceName(String serviceName) {
            this.serviceName = serviceName;
            return this;
        }

        public Builder httpMethodName(String httpMethodName) {
            this.httpMethodName = httpMethodName;
            return this;
        }

        public Builder canonicalURI(String canonicalURI) {
            this.canonicalURI = canonicalURI;
            return this;
        }

        public Builder queryParametes(TreeMap<String, String> queryParametes) {
            this.queryParametes = queryParametes;
            return this;
        }

        public Builder awsHeaders(TreeMap<String, String> awsHeaders) {
            this.awsHeaders = awsHeaders;
            return this;
        }

        public Builder payload(String payload) {
            this.payload = payload;
            return this;
        }

        public Builder debug() {
            this.debug = true;
            return this;
        }

        public AWSV4Auth build() {
            return new AWSV4Auth(this);
        }
    }

    private String accessKeyID;
    private String secretAccessKey;
    private String regionName;
    private String serviceName;
    private String httpMethodName;
    private String canonicalURI;
    private TreeMap<String, String> queryParametes;
    private TreeMap<String, String> awsHeaders;
    private String payload;
    private boolean debug = false;

    /* Other variables */
    private final String HMACAlgorithm = "AWS4-HMAC-SHA256";
    private final String aws4Request = "aws4_request";
    private String strSignedHeader;
    private String xAmzDate;
    private String currentDate;

    private AWSV4Auth(Builder builder) {
        accessKeyID = builder.accessKeyID;
        secretAccessKey = builder.secretAccessKey;
        regionName = builder.regionName;
        serviceName = builder.serviceName;
        httpMethodName = builder.httpMethodName;
        canonicalURI = builder.canonicalURI;
        queryParametes = builder.queryParametes;
        awsHeaders = builder.awsHeaders;
        payload = builder.payload;
        debug = builder.debug;

        /* Get current timestamp value.(UTC) */
        xAmzDate = getTimeStamp();
        currentDate = getDate();
    }

    /**
     * Task 1: Create a Canonical Request for Signature Version 4.
     *
     * @return
     */
    private String prepareCanonicalRequest() {
        StringBuilder canonicalURL = new StringBuilder("");

        /* Step 1.1 Start with the HTTP request method (GET, PUT, POST, etc.), followed by a newline character. */
        canonicalURL.append(httpMethodName).append("\n");

        /* Step 1.2 Add the canonical URI parameter, followed by a newline character. */
        canonicalURI = canonicalURI == null || canonicalURI.trim().isEmpty() ? "/" : canonicalURI;
        canonicalURL.append(canonicalURI).append("\n");

        /* Step 1.3 Add the canonical query string, followed by a newline character. */
        StringBuilder queryString = new StringBuilder("");
        if (queryParametes != null && !queryParametes.isEmpty()) {
            for (Map.Entry<String, String> entrySet : queryParametes.entrySet()) {
                String key = entrySet.getKey();
                String value = entrySet.getValue();
                queryString.append(key).append("=").append(encodeParameter(value)).append("&");
            }

            /* @co-author https://github.com/dotkebi @git #1 @date 16th March, 2017 */
            queryString.deleteCharAt(queryString.lastIndexOf("&"));

            queryString.append("\n");
        } else {
            queryString.append("\n");
        }
        canonicalURL.append(queryString);

        /* Step 1.4 Add the canonical headers, followed by a newline character. */
        StringBuilder signedHeaders = new StringBuilder("");
        if (awsHeaders != null && !awsHeaders.isEmpty()) {
            for (Map.Entry<String, String> entrySet : awsHeaders.entrySet()) {
                String key = entrySet.getKey();
                String value = entrySet.getValue();
                signedHeaders.append(key).append(";");
                canonicalURL.append(key).append(":").append(value).append("\n");
            }

            /* Note: Each individual header is followed by a newline character, meaning the complete list ends with a newline character. */
            canonicalURL.append("\n");
        } else {
            canonicalURL.append("\n");
        }

        /* Step 1.5 Add the signed headers, followed by a newline character. */
        strSignedHeader = signedHeaders.substring(0, signedHeaders.length() - 1); // Remove last ";"
        canonicalURL.append(strSignedHeader).append("\n");

        /* Step 1.6 Use a hash (digest) function like SHA256 to create a hashed value from the payload in the body of the HTTP or HTTPS. */
        payload = payload == null ? "" : payload;
        canonicalURL.append(generateHex(payload));

        if (debug) {
            System.out.println("##Canonical Request:\n" + canonicalURL.toString());
        }

        return canonicalURL.toString();
    }

    /**
     * Task 2: Create a String to Sign for Signature Version 4.
     *
     * @param canonicalURL
     * @return
     */
    private String prepareStringToSign(String canonicalURL) {
        String stringToSign = "";

        /* Step 2.1 Start with the algorithm designation, followed by a newline character. */
        stringToSign = HMACAlgorithm + "\n";

        /* Step 2.2 Append the request date value, followed by a newline character. */
        stringToSign += xAmzDate + "\n";

        /* Step 2.3 Append the credential scope value, followed by a newline character. */
        stringToSign += currentDate + "/" + regionName + "/" + serviceName + "/" + aws4Request + "\n";

        /* Step 2.4 Append the hash of the canonical request that you created in Task 1: Create a Canonical Request for Signature Version 4. */
        stringToSign += generateHex(canonicalURL);

        if (debug) {
            System.out.println("##String to sign:\n" + stringToSign);
        }

        return stringToSign;
    }

    /**
     * Task 3: Calculate the AWS Signature Version 4.
     *
     * @param stringToSign
     * @return
     */
    private String calculateSignature(String stringToSign) {
        try {
            /* Step 3.1 Derive your signing key */
            byte[] signatureKey = getSignatureKey(secretAccessKey, currentDate, regionName, serviceName);

            /* Step 3.2 Calculate the signature. */
            byte[] signature = HmacSHA256(signatureKey, stringToSign);

            /* Step 3.2.1 Encode signature (byte[]) to Hex */
            String strHexSignature = bytesToHex(signature);
            return strHexSignature;
        } catch (Exception ex) {
            ex.printStackTrace();
        }
        return null;
    }

    /**
     * Task 4: Add the Signing Information to the Request. We'll return Map of
     * all headers put this headers in your request.
     *
     * @return
     */
    public Map<String, String> getHeaders() {
        awsHeaders.put("x-amz-date", xAmzDate);

        /* Execute Task 1: Create a Canonical Request for Signature Version 4. */
        String canonicalURL = prepareCanonicalRequest();

        /* Execute Task 2: Create a String to Sign for Signature Version 4. */
        String stringToSign = prepareStringToSign(canonicalURL);

        /* Execute Task 3: Calculate the AWS Signature Version 4. */
        String signature = calculateSignature(stringToSign);

        if (signature != null) {
            Map<String, String> header = new HashMap<String, String>(0);
            header.put("x-amz-date", xAmzDate);
            header.put("Authorization", buildAuthorizationString(signature));

            if (debug) {
                System.out.println("##Signature:\n" + signature);
                System.out.println("##Header:");
                for (Map.Entry<String, String> entrySet : header.entrySet()) {
                    System.out.println(entrySet.getKey() + " = " + entrySet.getValue());
                }
                System.out.println("================================");
            }
            return header;
        } else {
            if (debug) {
                System.out.println("##Signature:\n" + signature);
            }
            return null;
        }
    }

    /**
     * Build string for Authorization header.
     *
     * @param strSignature
     * @return
     */
    private String buildAuthorizationString(String strSignature) {
        return HMACAlgorithm + " "
                + "Credential=" + accessKeyID + "/" + getDate() + "/" + regionName + "/" + serviceName + "/" + aws4Request + ","
                + "SignedHeaders=" + strSignedHeader + ","
                + "Signature=" + strSignature;
    }

    /**
     * Generate Hex code of String.
     *
     * @param data
     * @return
     */
    private String generateHex(String data) {
        MessageDigest messageDigest;
        try {
            messageDigest = MessageDigest.getInstance("SHA-256");
            messageDigest.update(data.getBytes("UTF-8"));
            byte[] digest = messageDigest.digest();
            return String.format("%064x", new java.math.BigInteger(1, digest));
        } catch (NoSuchAlgorithmException | UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * Apply HmacSHA256 on data using given key.
     *
     * @param data
     * @param key
     * @return
     * @throws Exception
     * @reference:
     * http://docs.aws.amazon.com/general/latest/gr/signature-v4-examples.html#signature-v4-examples-java
     */
    private byte[] HmacSHA256(byte[] key, String data) throws Exception {
        String algorithm = "HmacSHA256";
        Mac mac = Mac.getInstance(algorithm);
        mac.init(new SecretKeySpec(key, algorithm));
        return mac.doFinal(data.getBytes("UTF8"));
    }

    /**
     * Generate AWS signature key.
     *
     * @param key
     * @param date
     * @param regionName
     * @param serviceName
     * @return
     * @throws Exception
     * @reference
     * http://docs.aws.amazon.com/general/latest/gr/signature-v4-examples.html#signature-v4-examples-java
     */
    private byte[] getSignatureKey(String key, String date, String regionName, String serviceName) throws Exception {
        byte[] kSecret = ("AWS4" + key).getBytes("UTF8");
        byte[] kDate = HmacSHA256(kSecret, date);
        byte[] kRegion = HmacSHA256(kDate, regionName);
        byte[] kService = HmacSHA256(kRegion, serviceName);
        byte[] kSigning = HmacSHA256(kService, aws4Request);
        return kSigning;
    }

    final protected static char[] hexArray = "0123456789ABCDEF".toCharArray();

    /**
     * Convert byte array to Hex
     *
     * @param bytes
     * @return
     */
    private String bytesToHex(byte[] bytes) {
        char[] hexChars = new char[bytes.length * 2];
        for (int j = 0; j < bytes.length; j++) {
            int v = bytes[j] & 0xFF;
            hexChars[j * 2] = hexArray[v >>> 4];
            hexChars[j * 2 + 1] = hexArray[v & 0x0F];
        }
        return new String(hexChars).toLowerCase();
    }

    /**
     * Get timestamp. yyyyMMdd'T'HHmmss'Z'
     *
     * @return
     */
    private String getTimeStamp() {
        DateFormat dateFormat = new SimpleDateFormat("yyyyMMdd'T'HHmmss'Z'");
        dateFormat.setTimeZone(TimeZone.getTimeZone("UTC"));//server timezone
        return dateFormat.format(new Date());
    }

    /**
     * Get date. yyyyMMdd
     *
     * @return
     */
    private String getDate() {
        DateFormat dateFormat = new SimpleDateFormat("yyyyMMdd");
        dateFormat.setTimeZone(TimeZone.getTimeZone("UTC"));//server timezone
        return dateFormat.format(new Date());
    }

    /**
     * Using {@link URLEncoder#encode(java.lang.String, java.lang.String) } instead of
     * {@link URLEncoder#encode(java.lang.String) }
     * 
     * @co-author https://github.com/dotkebi
     * @date 16th March, 2017
     * @git #1
     * @param param
     * @return 
     */
     private String encodeParameter(String param){
         try {
             return URLEncoder.encode(param, "UTF-8");
         } catch (Exception e) {
             return URLEncoder.encode(param);
         }
     }
}

Source code (Test Class)

import java.util.Map;
import java.util.TreeMap;

/**
 * Example: Signing AWS Requests with Signature Version 4 in Java(Test class).
 * @reference: http://docs.aws.amazon.com/general/latest/gr/sigv4_signing.html
 * @author javaQuery
 * @date 19th January, 2016
 * @Github: https://github.com/javaquery/Examples
 */
public class AWSV4AuthTest {
    public static void main(String[] args) {
        String url = "xxxxx-yyyyy-r6nvlhpscgdwms5.ap-northeast-1.es.amazonaws.com/inventory/simple/123";
        
        /**
         * Add host without http or https protocol.
         * You can also add other parameters based on your amazon service requirement.
         */
        TreeMap<String, String> awsHeaders = new TreeMap<String, String>();
        awsHeaders.put("host", "xxxxx-yyyyy-r6nvlhpscgdwms5.ap-northeast-1.es.amazonaws.com");
        
        AWSV4Auth aWSV4Auth = new AWSV4Auth.Builder("exampleKey", "exampleSecret")
                                           .regionName("xx-yy-zzz")
                                           .serviceName("es") // es - elastic search. use your service name
                                           .httpMethodName("GET") //GET, PUT, POST, DELETE, etc...
                                           .canonicalURI("/inventory/simple/123") //end point
                                           .queryParametes(null) //query parameters if any
                                           .awsHeaders(awsHeaders) //aws header parameters
                                           .payload(null) // payload if any
                                           .debug() // turn on the debug mode
                                           .build();
        
        /* Get header calculated for request */
        Map<String, String> header = aWSV4Auth.getHeaders();
        for (Map.Entry<String, String> entrySet : header.entrySet()) {
            String key = entrySet.getKey();
            String value = entrySet.getValue();
            
            /* Attach header in your request */
            /* Simple get request */
            //HttpGet httpGet = new HttpGet(url);
            //httpGet.addHeader(key, value);
        }
        // execute httpGet
    }
}

Issue: One reader Rahul Lohagavkar facing 403(forbidden) in api call using above code.
Solution: Order(sequence) of query parameter should be same as defined in URL.
Note: I haven't tested this solution.

Tags: Amazon Web Services (AWS) , Security