KMS, ACM 및 암호화 패턴

AWS 암호화 개요

# Encryption coverage on AWS:
# At rest (KMS):
#   S3, EBS, RDS, DynamoDB, EFS, SQS,
#   Lambda env vars, Secrets Manager, SSM Parameter Store

# In transit (ACM/TLS):
#   ALB listeners (HTTPS), API Gateway, CloudFront,
#   Direct Connect, VPN, inter-service communication

# Both:
#   S3 Server-Side Encryption + HTTPS only policy

AWS KMS: 키 관리 서비스

# Create a Customer Managed Key (CMK)
aws kms create-key \
  --description 'Production database encryption key' \
  --key-usage ENCRYPT_DECRYPT \
  --origin AWS_KMS \
  --tags TagKey=Purpose,TagValue=RDS-Encryption

# Create an alias for the key
aws kms create-alias \
  --alias-name alias/prod-db-key \
  --target-key-id arn:aws:kms:us-east-1:123:key/abc-def

# CMK costs: $1/month + $0.03 per 10,000 API calls

KMS 키 정책 및 권한 부여

# KMS key policy: grant RDS and admin access
{
  'Statement': [
    {
      'Sid': 'Enable root account full access',
      'Principal': {'AWS': 'arn:aws:iam::123:root'},
      'Action': 'kms:*',
      'Effect': 'Allow'
    },
    {
      'Sid': 'Allow RDS to use this key',
      'Principal': {'Service': 'rds.amazonaws.com'},
      'Action': ['kms:Encrypt','kms:Decrypt','kms:GenerateDataKey'],
      'Effect': 'Allow'
    }
  ]
}

KMS 봉투 암호화

# Generate a Data Key (for envelope encryption)
aws kms generate-data-key \
  --key-id alias/my-key \
  --key-spec AES_256

# Response contains:
# Plaintext: base64-encoded DEK (use to encrypt data locally)
# CiphertextBlob: KMS-encrypted DEK (store alongside data)

# To decrypt:
# 1. Call kms:Decrypt(CiphertextBlob) -> plaintext DEK
# 2. Use plaintext DEK to decrypt data locally
# 3. Zeroize plaintext DEK from memory
aws kms decrypt --ciphertext-blob fileb://encrypted-dek.bin

KMS 키 rotation

# Enable automatic annual key rotation
aws kms enable-key-rotation \
  --key-id alias/prod-db-key

# Verify rotation is enabled
aws kms get-key-rotation-status \
  --key-id alias/prod-db-key

# Manual rotation (for imported key material):
# 1. Create a new CMK
# 2. Update all services to use new key
# 3. Re-encrypt existing data with new key
# 4. Schedule old key for deletion (minimum 7-day waiting period)

S3 서버 측 암호화 옵션

# Enforce SSE-KMS on all new S3 objects
aws s3api put-bucket-policy \
  --bucket my-secure-bucket \
  --policy '{
    "Statement": [{
      "Effect": "Deny",
      "Principal": "*",
      "Action": "s3:PutObject",
      "Resource": "arn:aws:s3:::my-secure-bucket/*",
      "Condition": {
        "StringNotEquals": {
          "s3:x-amz-server-side-encryption": "aws:kms"
        }
      }
    }]
  }'

# Set default encryption for bucket
aws s3api put-bucket-encryption \
  --bucket my-secure-bucket \
  --server-side-encryption-configuration '{"Rules":[{"ApplyServerSideEncryptionByDefault":{"SSEAlgorithm":"aws:kms","KMSMasterKeyID":"alias/my-key"}}]}'

AWS Certificate Manager(ACM)

# Request a public ACM certificate
aws acm request-certificate \
  --domain-name app.example.com \
  --subject-alternative-names '*.example.com' \
  --validation-method DNS

# ACM returns a CNAME record to add to Route 53
# Add the CNAME -> ACM validates domain ownership
# Certificate is issued and auto-renews annually

# Attach to ALB listener (HTTPS:443)
aws elbv2 create-listener \
  --load-balancer-arn <ALB-ARN> \
  --protocol HTTPS --port 443 \
  --certificates CertificateArn=arn:aws:acm:us-east-1:123:certificate/abc \
  --default-actions Type=forward,TargetGroupArn=<TG-ARN>

ACM Private Certificate Authority

# Create ACM Private Certificate Authority
aws acm-pca create-certificate-authority \
  --certificate-authority-type ROOT \
  --certificate-authority-configuration '{
    "KeyAlgorithm": "RSA_2048",
    "SigningAlgorithm": "SHA256WITHRSA",
    "Subject": {
      "Country": "US",
      "Organization": "Example Corp",
      "CommonName": "Example Corp Internal CA"
    }
  }'

# Issue certificate from private CA
aws acm request-certificate \
  --domain-name internal-service.example.internal \
  --certificate-authority-arn arn:aws:acm-pca:us-east-1:123:certificate-authority/xxx

EBS 및 RDS Encryption

# Enable account-level EBS default encryption
aws ec2 enable-ebs-encryption-by-default
aws ec2 modify-ebs-default-kms-key-id \
  --kms-key-id alias/prod-ebs-key

# Encrypt an existing unencrypted RDS instance:
# 1. Create unencrypted snapshot
aws rds create-db-snapshot \
  --db-instance-identifier mydb \
  --db-snapshot-identifier mydb-plain-snapshot

# 2. Copy snapshot with encryption
aws rds copy-db-snapshot \
  --source-db-snapshot-identifier mydb-plain-snapshot \
  --target-db-snapshot-identifier mydb-encrypted-snapshot \
  --kms-key-id alias/prod-db-key

Client-Side Encryption과 Server-Side Encryption 비교

# Client-side encryption with AWS Encryption SDK
# (conceptual Python example)

# 1. Application encrypts data locally using KMS DEK
# from aws_encryption_sdk import KmsKeyProvider, encrypt

# key_provider = KmsKeyProvider(key_ids=['alias/my-key'])
# ciphertext, _ = encrypt(
#     source=b'Sensitive patient data',
#     key_provider=key_provider
# )

# 2. Send ciphertext to S3
# s3.put_object(Bucket='hipaa-data', Key='record.enc', Body=ciphertext)

# AWS only stores ciphertext - cannot decrypt without your key policy

KMS 계정 간 액세스

# KMS key policy: allow cross-account access
# (in Account A's key policy)
{
  'Sid': 'Allow Account B to use this key',
  'Effect': 'Allow',
  'Principal': {
    'AWS': 'arn:aws:iam::999999999999:root'
  },
  'Action': [
    'kms:Encrypt',
    'kms:Decrypt',
    'kms:ReEncrypt*',
    'kms:GenerateDataKey*',
    'kms:DescribeKey'
  ],
  'Resource': '*'
}

# Account B IAM policy also needed to allow the role to use it

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