ALB/NLB now supports Post-Quantum Key Exchange.

In November 2025, there was an update to Application Load Balancer (ALB) and Network Load Balancer (NLB) that added support for Post-Quantum Key Exchange.

https://aws.amazon.com/jp/about-aws/whats-new/2025/11/network-load-balancers-post-quantum-key-exchange-tls/

While practical quantum computers may still be some time away, there is a risk of HNDL (Harvest Now, Decrypt Later) / SNDL (Store Now, Decrypt Later) attacks, where encrypted communication data is intercepted and stored now to be decrypted later when high-performance quantum computers become available.

https://aws.amazon.com/jp/security/post-quantum-cryptography/

With ALB and NLB now supporting new cryptographic methods (post-quantum cryptography) that are difficult to decrypt even with quantum computers, it's possible to prepare for the risk of future data decryption.

I recently had the opportunity to create ALB and NLB with post-quantum cryptography support using CloudFormation and test their functionality with browser connections, which I'd like to share.

Test Environment

Architecture Diagram

ALB

I configured the security policy "ELBSecurityPolicy-TLS13-1-2-Res-PQ-2025-09," which includes "PQ" indicating post-quantum cryptography support.

  Listener:
    Type: AWS::ElasticLoadBalancingV2::Listener
    Properties:
      LoadBalancerArn: !Ref LoadBalancer
      Port: 443
      Protocol: HTTPS
      Certificates:
        - CertificateArn: !Ref CertificateArn
      SslPolicy: ELBSecurityPolicy-TLS13-1-2-Res-PQ-2025-09 

• In the management console, I used "ELBSecurityPolicy-TLS13-1-2-Res-PQ-2025-09" which was listed as recommended among the PQ-supported post-quantum TLS policies.

ACM (AWS Certificate Manager)

For the TLS/SSL certificate, I used one created with the key algorithm "ECDSA P 256".

CloudFormation

I used the following template to build the ALB and EC2 for testing.

AWSTemplateFormatVersion: '2010-09-09'
Description: 'ALB Post-Quantum TLS Test Environment (ARM64/T4g)'

Parameters:
  VpcId:
    Type: AWS::EC2::VPC::Id
    Description: Default VPC ID

  SubnetIds:
    Type: List<AWS::EC2::Subnet::Id>
    Description: Select at least 2 Public Subnets

  CertificateArn:
    Type: String
    Description: ACM Certificate ARN for HTTPS Listener
    Default: arn:aws:acm:ap-northeast-1:********:certificate/****-***-***-***-******
    AllowedPattern: "arn:aws:acm:.*"

  LatestAmiId:
    Type: AWS::SSM::Parameter::Value<AWS::EC2::Image::Id>
    Default: /aws/service/ami-amazon-linux-latest/al2023-ami-kernel-default-arm64

Resources:
  # Security Group
  ALBSecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Allow HTTPS
      VpcId: !Ref VpcId
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: 443
          ToPort: 443
          CidrIp: 0.0.0.0/0

  EC2SecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Allow HTTP from ALB
      VpcId: !Ref VpcId
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: 80
          ToPort: 80
          SourceSecurityGroupId: !Ref ALBSecurityGroup

  # EC2 Instance
  TargetInstance:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: !Ref LatestAmiId
      InstanceType: t4g.nano
      SecurityGroupIds:
        - !Ref EC2SecurityGroup
      SubnetId: !Select [0, !Ref SubnetIds]
      UserData:
        Fn::Base64: !Sub |
          #!/bin/bash
          yum update -y
          yum install -y httpd
          systemctl start httpd
          systemctl enable httpd
          echo "<h1>Post-Quantum TLS Test (ARM)</h1>" > /var/www/html/index.html
      Tags:
        - Key: Name
          Value: ALB-PQ-Target-ARM

  # Target Group
  TargetGroup:
    Type: AWS::ElasticLoadBalancingV2::TargetGroup
    Properties:
      Name: alb-pq-test-tg
      Port: 80
      Protocol: HTTP
      VpcId: !Ref VpcId
      Targets:
        - Id: !Ref TargetInstance

  # ALB
  LoadBalancer:
    Type: AWS::ElasticLoadBalancingV2::LoadBalancer
    Properties:
      Name: alb-pq-test
      Scheme: internet-facing
      SecurityGroups:
        - !Ref ALBSecurityGroup
      Subnets: !Ref SubnetIds

  # HTTPS Listener with PQ Policy
  Listener:
    Type: AWS::ElasticLoadBalancingV2::Listener
    Properties:
      LoadBalancerArn: !Ref LoadBalancer
      Port: 443
      Protocol: HTTPS
      Certificates:
        - CertificateArn: !Ref CertificateArn
      SslPolicy: ELBSecurityPolicy-TLS13-1-2-Res-PQ-2025-09 
      DefaultActions:
        - Type: forward
          TargetGroupArn: !Ref TargetGroup

Connection Verification

Chrome

I attempted to verify using the developer tools in Google Chrome, version 142.0.7444.176 (Official Build) (arm64).

In the Connection - secure connection settings section, I confirmed the use of MLKEM768: a quantum-resistant cryptographic algorithm standardized by NIST (Module-Lattice-Based Key-Encapsulation Mechanism, formerly Kyber).

SSL Labs

I also attempted verification using SSL Labs' SSL Server Test.

As of November 2025, the SSL Server Test does not support quantum-resistant cryptographic algorithms (PQ), so PQ connections could not be verified.

However, connections using X25519 (traditional elliptic curve cryptography) were successful with an "A" rating, confirming that existing clients without PQ support can still access the system without issues.

Summary

By simply changing the security policy of ALB/NLB, it's now possible to protect against HNDL/SNDL attacks. For systems in finance, healthcare, public sectors, etc., where confidentiality must be maintained for years or decades, this implementation is worth considering.

The performance impact of using hybrid key exchange is limited to an increase in TLS handshake message size by about 1KB. The ML-KEM (lattice cryptography) used is actually much faster in computation compared to traditional RSA or elliptic curve cryptography, resulting in minimal impact on CPU resource consumption for ELBs and browsers.

In the future, if countermeasures against HNDL/SNDL attacks are required, please consider using the post-quantum key exchange (PQ) policy now supported by ALB/NLB.