Encrypting and decrypting strings using AWS Key Management Service (KMS) and the AWS Command Line Interface (CLI) is a crucial part of securing sensitive data in your AWS environment. In this blog post, we'll walk through the process of encrypting and decrypting a string using KMS and the AWS CLI. This is a fundamental skill for protecting your data in AWS services like S3, RDS, and Lambda.

Requirement

• You will need AWS CLI, You can follow this doc to install it, https://docs.aws.amazon.com/cli/latest/userguide/getting-started-install.html

• You can follow this guide to create the KMS key, https://docs.aws.amazon.com/kms/latest/developerguide/create-keys.html

Encrypting String

• Let's create a simple plaintext string for encryption purposes.

echo "Hello World" > hello.txt

• Let's run the following command to encrypt our string. If you notice we are outputting it to encrypted.base64 because AWS CLI will encrypt it and then encode it into base64.

aws kms encrypt --key-id <KMS_ID> \
  --plaintext fileb://hello.txt \
  --output text --query CiphertextBlob > encrypted.bas64

Now this string is safe to store as only the KMS key can decrypt this.

Decrypting String

• For decrypting the string, let's first decode the base64 string. If you check the content of encrypted, it will be a binary blob.

cat encrypted.base64 | base64 --decode > encrypted

• Let's AWS CLI to decrypt the base64 decoded encrypted. You will get another base64 string

aws kms decrypt --ciphertext-blob fileb://encrypted --output text --query Plaintext --key-id <KMS_ID> --region eu-west-2
SGVsbG8gV29ybGQK

• Now we just need to decode the string to get our data string.

echo "SGVsbG8gV29ybGQK" | base64 --decode
Hello World

• You can combine the above 2 commands in one command and output the text into a file.

aws kms decrypt --ciphertext-blob fileb://encrypted --output text --query Plaintext --key-id <KMS_ID> --region eu-west-2 | base64 --decode > decrypted.tx

In this blog post, we've learned how to encrypt and decrypt a string using AWS KMS and the AWS CLI.

Remember to manage your KMS keys carefully, control access with IAM policies, and follow AWS security best practices to maintain a robust security posture in your AWS environment.