Digital signature and its verification based on data hash

In Key Management Service, you can create a digital signature that can be used to validate data authenticity and integrity, as well as to protect signed data from editing.

Getting startedGetting started

In this tutorial, digital signature verification is performed using the OpenSSL utility. If you do not have OpenSSL yet, install it.

sudo apt-get install openssl

choco install openssl

Create a digital signatureCreate a digital signature

Depending on the size of a signed message or file, KMS allows creating a message signature based on a private key or a signature based on data hash.

Message signature based on a private keyMessage signature based on a private key

1. If you do not have a digital signature key pair, create one.

2. Get a public signature key and save it:

   Management console

   CLI

   1. In the management console, select the folder with the appropriate digital signature key pair.
   2. In the list of services, select Key Management Service.
   3. In the left-hand panel, select Asymmetric keys.
   4. Go to the Signature tab.
   5. In the row with the appropriate key pair, click and select Public key.
   6. In the window that opens, click Download to download the digital signature public key.

   If you do not have the Yandex Cloud command line interface yet, install and initialize it.

   The folder specified in the CLI profile is used by default. You can specify a different folder using the --folder-name or --folder-id parameter.

   1. View the description of the CLI command to get a signature public key:

      yc kms asymmetric-signature-crypto get-public-key --help
      

   2. Get the ID of the folder where the digital signature key pair is saved.

   3. Get the ID of the required digital signature key pair by specifying the folder ID:

      yc kms asymmetric-signature-key list \
        --folder-id <folder_ID>
      

      Result:

      +----------------------+----------------------+---------------------------+---------------------+--------+
      |          ID          |         NAME         |    SIGNATURE ALGORITHM    |     CREATED AT      | STATUS |
      +----------------------+----------------------+---------------------------+---------------------+--------+
      | abj9g2dil5sj******** | sample-signature-key | RSA_2048_SIGN_PSS_SHA_512 | 2023-08-16 09:06:57 | ACTIVE |
      +----------------------+----------------------+---------------------------+---------------------+--------+
      

   4. Get a digital signature public key by specifying the previously obtained key pair ID:

      yc kms asymmetric-signature-crypto get-public-key \
        --id <key_pair_ID>
      

      Result:

      key_id: abj9g2dil5sj********
      public_key: |
      -----BEGIN PUBLIC KEY-----
      MIIB...
      ...QAB
      -----END PUBLIC KEY-----
      

      Save the obtained key to a file, such as public.key. Make sure that lines in the file do not start with spaces.

3. Create a file with a base64-encoded message:

   1. Create a text file, e.g., message.txt:

      cat > message.txt
      My sample message.
      It will be used to verify ECDSA signature.
      

      The message size must not exceed 32 KB.

   2. Change the message encoding to base64 by specifying the path to the created message file in base64:

      base64 message.txt > <base64_message_file>
      

4. Create a message signature:

   CLI

   1. View the description of the CLI command to get a digital signature:

      yc kms asymmetric-signature-crypto sign --help
      

   2. Get the message's digital signature:

      yc kms asymmetric-signature-crypto sign \
        --id <key_pair_ID> \
        --signature-output-file <signature_file_path> \
        --message-file <message_file_path> \
        --inform base64 \
        --outform base64
      

      Where:

      • --id: ID of the digital signature key pair.
      • --signature-output-file: Path to the file to save the digital signature to.
      • --message-file: Path to the previously created file with the base64-encoded message.
      • --inform: Message file format. Possible values: raw (default), base64, and hex.
      • --outform: Signature file format. Possible values: raw (default), base64, and hex.

      Result:

      key_id: abjcg4mhmdfe********
      signature: MAa7C...imw==
      

   3. Change the format of the resulting digital signature to DER (this format is required for OpenSSL):

      echo -n "$(< <signature_file_path>)" | base64 -d > <signature_file>
      

      Where:

      • <signature_file_path>: Path to the signature file created at the previous step.
      • <signature_file>: Path to the new signature file in DER format.

   The DER signature file you get can be used to verify the signature using OpenSSL.

File signature based on data hashFile signature based on data hash

1. If you do not have a digital signature key pair, create one.

2. Get a digital signature public key and save it:

   Management console

   CLI

   1. In the management console, select the folder with the appropriate digital signature key pair.
   2. In the list of services, select Key Management Service.
   3. In the left-hand panel, select Asymmetric keys.
   4. Go to the Signature tab.
   5. In the row with the appropriate key pair, click and select Public key.
   6. In the window that opens, click Download to download the signature public key.

   If you do not have the Yandex Cloud command line interface yet, install and initialize it.

   The folder specified in the CLI profile is used by default. You can specify a different folder using the --folder-name or --folder-id parameter.

   1. View the description of the CLI command to get a signature public key:

      yc kms asymmetric-signature-crypto get-public-key --help
      

   2. Get the ID of the folder where the digital signature key pair is saved.

   3. Get the ID of the required digital signature key pair by specifying the folder ID:

      yc kms asymmetric-signature-key list \
        --folder-id <folder_ID>
      

      Result:

      +----------------------+----------------------+---------------------------+---------------------+--------+
      |          ID          |         NAME         |    SIGNATURE ALGORITHM    |     CREATED AT      | STATUS |
      +----------------------+----------------------+---------------------------+---------------------+--------+
      | abj9g2dil5sj******** | sample-signature-key | RSA_2048_SIGN_PSS_SHA_512 | 2023-08-16 09:06:57 | ACTIVE |
      +----------------------+----------------------+---------------------------+---------------------+--------+
      

   4. Get a digital signature public key by specifying the previously obtained key pair ID:

      yc kms asymmetric-signature-crypto get-public-key \
        --id <key_pair_ID>
      

      Result:

      key_id: abj9g2dil5sj********
      public_key: |
      -----BEGIN PUBLIC KEY-----
      MIIB...
      ...QAB
      -----END PUBLIC KEY-----
      

      Save the obtained key to a file, such as public.key. Make sure that lines in the file do not start with spaces.

3. Get a file's hash:

   Bash

   PowerShell

   Run this command:

   echo -n \
     $(<hashing_algorithm> <source_file_path> | cut -d " " -f 1) > \
     <hash_file_path>
   

   Where:

   • <hashing_algorithm>: Hashing algorithm used when creating a digital signature key pair. The hashing algorithm is specified above in the SIGNATURE ALGORITHM field of the results you get with the list of key pairs. The possible values are:
     • sha256sum: For SHA-256 algorithms.
     • sha384sum: For SHA-384 algorithms.
     • sha512sum: For SHA-512 algorithms.
   • <source_file_path>: Path to the file whose hash you want to get.
   • <hash_file_path>: Path to the file to save the hash to.

   Run this command:

   (Get-FileHash -Path <source_file_path> -Algorithm <hashing_algorithm>).Hash.ToLower() | `
     Out-File -FilePath <hash_file_path> `
     -encoding ASCII `
     -NoNewline
   

   Where:

   • <hashing_algorithm>: Hashing algorithm used when creating a signature key pair. The hashing algorithm is specified above in the SIGNATURE ALGORITHM field of the results you get with the list of key pairs. The possible values are:
     • SHA256: For SHA-256 algorithms.
     • SHA384: For SHA-384 algorithms.
     • SHA512: For SHA-512 algorithms.
   • <source_file_path>: Path to the file whose hash you want to get.
   • <hash_file_path>: Path to the file to save the hash to.

4. Create a hash-based file signature:

   CLI

   1. View the description of the CLI command to get a hash-based digital signature:

      yc kms asymmetric-signature-crypto sign-hash --help
      

   2. Get the ID of the folder where the digital signature key pair is saved.

   3. Get the ID of the required digital signature key pair by specifying the folder ID:

      yc kms asymmetric-signature-key list \
        --folder-id <folder_ID>
      

      Result:

      +----------------------+----------------------+---------------------------+---------------------+--------+
      |          ID          |         NAME         |    SIGNATURE ALGORITHM    |     CREATED AT      | STATUS |
      +----------------------+----------------------+---------------------------+---------------------+--------+
      | abj9g2dil5sj******** | sample-signature-key | RSA_2048_SIGN_PSS_SHA_512 | 2023-08-16 09:06:57 | ACTIVE |
      +----------------------+----------------------+---------------------------+---------------------+--------+
      

   4. Get a hash-based digital signature:

      yc kms asymmetric-signature-crypto sign-hash \
        --id <key_pair_ID> \
        --signature-output-file <signature_file_path> \
        --message-hash-file <hash_file_path> \
        --inform hex
      

      Where:

      • --id: ID of the digital signature key pair.
      • --signature-output-file: Path to the file to save the digital signature to.
      • --message-hash-file: Path to the previously created hash file.
      • --inform: Hash file format. The example uses the common hex format that is supported by all platforms. Possible values: raw (default), base64, and hex.

      Result:

      signature: W7V8A...22g==
      

Verify the digital signatureVerify the digital signature

ECDSA signatureECDSA signature

openssl dgst \
  -<hashing_algorithm> \
  -verify <path_to_public_key_file> \
  -signature <path_to_signature_file> \
  <path_to_signed_file>

import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.util.io.pem.PemObject;
import org.bouncycastle.util.io.pem.PemReader;

import javax.crypto.BadPaddingException;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import java.io.IOException;
import java.io.StringReader;
import java.security.*;
import java.security.spec.*;
import java.util.Base64;

import org.bouncycastle.jce.provider.BouncyCastleProvider;

public class VerifyEcdsaSign {

    public static void main(String[] args) throws Exception {
        String publicKeyPem =
        """
        -- -- - BEGIN PUBLIC KEY-- -- -
        <public_key_contents>
            -- -- - END PUBLIC KEY-- -- -
        """;
        String signatureStr = "<signature_string>";
        byte[] signatureDer = Base64.getDecoder().decode(signatureStr);
        System.out.println(verifyEcdsaSignature(publicKeyPem, signatureDer, "<message_string>", "<algorithm_type>"));
    }

    public static boolean verifyEcdsaSignature(String publicKeyPem, byte[] signatureDer, String message, String hash_algorithm)
    throws NoSuchAlgorithmException, InvalidKeySpecException, InvalidKeyException,
    SignatureException, IOException {

        // Public key and subscription decoding
        PemReader pemReader = new PemReader(new StringReader(publicKeyPem));
        PemObject pemObject = pemReader.readPemObject();
        byte[] publicKeyBytes = pemObject.getContent();

        // Creating a PublicKey object from the decoded public key
        KeyFactory keyFactory = KeyFactory.getInstance("EC", new BouncyCastleProvider());
        EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(publicKeyBytes);
        PublicKey publicKey = keyFactory.generatePublic(publicKeySpec);

        // Creating a Signature object and initializing it with a public key
        Signature signature = Signature.getInstance(hash_algorithm + "withECDSA", new BouncyCastleProvider());
        signature.initVerify(publicKey);

        // Updating a Signature Object with Message Data
        byte[] messageBytes = message.getBytes();
        signature.update(messageBytes);

        // Signature verification using original message and decoded signature
        return signature.verify(signatureDer);
    }
}

import (
    "crypto/ecdsa"
    "crypto/sha256"
    "crypto/x509"
    "encoding/asn1"
    "encoding/base64"
    "encoding/pem"
    "fmt"
    "hash"
    "log"
    "math/big"
)

func runEcdsaSignTest() {
    publicKeyPem := `-----BEGIN PUBLIC KEY-----
    <public_key_contents>
    -----END PUBLIC KEY-----`
    signatureB64 := "<signature_string>"
    signatureDER, _ := base64.StdEncoding.DecodeString(signatureB64)
    message := "<message_string>"

        fmt.Println(verifyEcdsa(publicKeyPem, signatureDER, message, <algorithm_type>))
}

type ECDSASignature struct {
    R, S *big.Int
}

func verifyEcdsa(publicKeyPem string, signatureDER []byte, message string, hashFunc hash.Hash) bool {

    // Decode the public key
    block, _ := pem.Decode([]byte(publicKeyPem))
    if block == nil {
        log.Fatal("failed to decode PEM block containing public key")
    }

    // Parse the public key
    pub, err := x509.ParsePKIXPublicKey(block.Bytes)
    if err != nil {
	    log.Fatal(err)
    }

    publicKey, ok := pub.(*ecdsa.PublicKey)
    if !ok {
	    log.Fatal("not ECDSA public key")
    }

    // Parse the signature
    var signature ECDSASignature
    _, err = asn1.Unmarshal(signatureDER, &signature)
    if err != nil {
	    log.Fatal(err)
    }

    // Compute the hash of the message
    hashFunc.Write([]byte(message))
    hashed := hashFunc.Sum(nil)

    // Verify the signature
    return ecdsa.Verify(publicKey, hashed, signature.R, signature.S)
}

import base64
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import ec
from cryptography.hazmat.primitives import hashes
from cryptography.exceptions import InvalidSignature
from cryptography.hazmat.backends import default_backend

# Define hash algorithms
def verify_ecdsa_signature(public_key_b64, signature_der, message, hash_algorithm):
    hash_algorithms = {
        'SHA256': hashes.SHA256,
        'SHA384': hashes.SHA384,
        'SHA512': hashes.SHA512
    }

    # Check if the provided hash algorithm is supported
    if hash_algorithm not in hash_algorithms:
        raise ValueError('Unsupported hash algorithm: ' + hash_algorithm)

    # Loading a PEM Encoded Public Key
    public_key = serialization.load_pem_public_key(
        public_key_b64.encode(),
        backend = default_backend()
    )

    # Create Signature object and initialize it with the public key
    signature = ec.ECDSA(hash_algorithms[hash_algorithm]())

    # Update the Signature object with the message data
    message_bytes = message.encode()

    # Verify the signature using the original message and the decoded signature
    try:
        public_key.verify(signature_der, message_bytes, signature)
        return True
    except InvalidSignature:
        return False

def test_verify_signature():
    public_key_b64 = """
    -----BEGIN PUBLIC KEY-----
    <public_key_content>
    -----END PUBLIC KEY-----"""
    signature_b64 = "<signature>"
    signature_der = base64.b64decode(signature_b64)
    message = '<message>'
    print(verify_ecdsa_signature(public_key_b64, signature_der, message, "<algorithm_type>"))

RSA signatureRSA signature

openssl dgst \
  -<hashing_algorithm> \
  -sigopt rsa_padding_mode:pss \
  -sigopt rsa_pss_saltlen:-1 \
  -verify <path_to_public_key_file> \
  -signature <path_to_signature_file> \
  <path_to_signed_file>

import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.util.io.pem.PemObject;
import org.bouncycastle.util.io.pem.PemReader;

import javax.crypto.BadPaddingException;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import java.io.IOException;
import java.io.StringReader;
import java.security.*;
import java.security.spec.*;
import java.util.Base64;

public class VerifyRsaSign {

    public static void main(String[] args) throws Exception {
        String publicKeyPem = """
        -----BEGIN PUBLIC KEY-----
        <public_key_contents>
        -----END PUBLIC KEY-----""";
        String signatureStr = "<signature_string>";
        byte[] signatureBytes = Base64.getDecoder().decode(signatureStr);
        String message = "<message_string>";
        System.out.println(verifyRsaSignature(publicKeyPem, signatureBytes, message, "<algorithm_type>"));
    }

    private static boolean verifyRsaSignature(String publicKeyPem, byte[] signatureBytes, String message, String hashAlgorithm)
    throws NoSuchAlgorithmException, InvalidKeySpecException, InvalidKeyException,
    SignatureException, InvalidAlgorithmParameterException, IOException {

        // Get the public key
        PemReader pemReader = new PemReader(new StringReader(publicKeyPem));
        PemObject pemObject = pemReader.readPemObject();
        byte[] publicKeyBytes = pemObject.getContent();

        // Create a PublicKey object using the decoded public key
        KeyFactory keyFactory = KeyFactory.getInstance("RSA", new BouncyCastleProvider());
        EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(publicKeyBytes);
        PublicKey pubKey = keyFactory.generatePublic(publicKeySpec);

        MessageDigest messageDigest = MessageDigest.getInstance(hashAlgorithm);
        int saltLength = messageDigest.getDigestLength();

        // Initialize the PSS signer
        PSSParameterSpec pssSpec = new PSSParameterSpec(hashAlgorithm, "MGF1", new MGF1ParameterSpec(hashAlgorithm), saltLength, 1);
        Signature signer = Signature.getInstance("RSASSA-PSS");
        signer.setParameter(pssSpec);
        signer.initVerify(pubKey);

        // Update the signature with the hash of the message
        byte[] messageBytes = message.getBytes();
        signer.update(messageBytes);

        // Verify the signature
        return signer.verify(signatureBytes);
    }
}

import (
    "crypto"
    "crypto/rsa"
    "crypto/sha256"
    "crypto/x509"
    "encoding/base64"
    "encoding/pem"
    "fmt"
    "log"
)

func runRsaSignTest() {
    publicKeyB64 := "<public_key_contents>"
    signatureB64 := "<signature_string>"
    signatureBytes, _ := base64.StdEncoding.DecodeString(signatureB64)
    message := "<message_string>"

        fmt.Println(verifyRsa(publicKeyB64, signatureBytes, message, <algorithm_type>))
}

func verifyRsa(publicKeyPem string, signatureBytes []byte, message string, hash crypto.Hash) bool {

    // Decode the public key
    block, _ := pem.Decode([]byte(publicKeyPem))
    if block == nil {
        log.Fatal("failed to decode PEM block containing public key")
    }

    // Parse the public key
    pub, err := x509.ParsePKIXPublicKey(block.Bytes)
    if err != nil {
	    log.Fatal(err)
    }

    publicKey, ok := pub.(*rsa.PublicKey)
    if !ok {
	    log.Fatal("not RSA public key")
    }

    // Calculate the hash of the message
    hasher := hash.New()
    hasher.Write([]byte(message))
    hashed := hasher.Sum(nil)

    // Set the PSS options: salt length auto, and the hash function
    pssOptions := &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthAuto, Hash: hash}

    // Verify the signature
    err = rsa.VerifyPSS(publicKey, hash, hashed, signatureBytes, pssOptions)
    if err != nil {
	    fmt.Println("Verification failed:", err)
	    return false
    } else {
	    return true
    }
}

import base64
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.asymmetric import padding
from cryptography.hazmat.primitives import serialization
from cryptography.exceptions import InvalidSignature
from cryptography.hazmat.backends import default_backend

# Define hash algorithms and corresponding salt lengths
def verify_rsa_signature(public_key_b64, signature_bytes, message, hash_algorithm):
    hash_algorithms = {
        'SHA256': hashes.SHA256,
        'SHA384': hashes.SHA384,
        'SHA512': hashes.SHA512
    }

    # Check if the provided hash algorithm is supported
    if hash_algorithm not in hash_algorithms:
        raise ValueError('Unsupported hash algorithm: ' + hash_algorithm)

    # Loading a PEM Encoded Public Key
    public_key = serialization.load_pem_public_key(
        public_key_b64.encode(),
        backend=default_backend()
    )

    # Update the Signature object with the message data
    message_bytes = message.encode()

    # Automatically calculate salt length based on hash digest size
    salt_length = hash_algorithms[hash_algorithm]().digest_size

    # Verify the signature using the original message and the decoded signature
    try:
        public_key.verify(
            signature_bytes,
            message_bytes,
            padding.PSS(
                mgf = padding.MGF1(hash_algorithms[hash_algorithm]()),
                salt_length = salt_length
            ),
            hash_algorithms[hash_algorithm]()
        )
        return True
    except InvalidSignature:
        return False

def test_verify_signature():
    public_key_b64 = """
    -----BEGIN PUBLIC KEY-----
    <public_key_contents>
    -----END PUBLIC KEY-----"""
    signature_b64 = '<signature>'
    signature_bytes = base64.b64decode(signature_b64)
    message = '<message>'
    print(verify_rsa_signature(public_key_b64, signature_bytes, message, '<algorithm_type>'))