How to Encrypt Data Using AWS KMS: Simple Guide

To encrypt data using AWS KMS, you call the Encrypt API with your plaintext and the KMS key ID. AWS KMS returns the encrypted ciphertext, which you can store securely. This process protects your data using strong encryption managed by AWS.

Syntax

The basic syntax to encrypt data with AWS KMS involves calling the Encrypt API with two main inputs:

• KeyId: The identifier of the KMS key to use for encryption.
• Plaintext: The raw data you want to encrypt.

The API returns CiphertextBlob, which is the encrypted data.

bash

aws kms encrypt --key-id <key-id> --plaintext fileb://plaintext.txt --output text --query CiphertextBlob | base64 --decode > encrypted.dat

Example

This example shows how to encrypt a simple text string using AWS KMS with the AWS CLI. It encrypts the text and saves the encrypted output to a file.

bash

echo "Hello, KMS encryption!" > plaintext.txt
aws kms encrypt --key-id alias/my-key --plaintext fileb://plaintext.txt --output text --query CiphertextBlob | base64 --decode > encrypted.dat
file encrypted.dat

Output

encrypted.dat: data

Common Pitfalls

Common mistakes when encrypting data with KMS include:

• Using the wrong KeyId or alias that does not exist or lacks permissions.
• Passing plaintext incorrectly, such as forgetting to use fileb:// prefix for binary data.
• Not handling the base64 encoding/decoding properly, which can corrupt the encrypted output.
• Trying to encrypt data larger than the KMS limit (4 KB); for large data, use envelope encryption.

bash

aws kms encrypt --key-id alias/wrong-key --plaintext fileb://plaintext.txt
# This will fail if the key alias is incorrect or you lack permissions

# Correct usage example:
aws kms encrypt --key-id alias/my-key --plaintext fileb://plaintext.txt --output text --query CiphertextBlob | base64 --decode > encrypted.dat

Quick Reference

Parameter	Description
KeyId	The KMS key ID or alias to use for encryption
Plaintext	The raw data to encrypt (max 4 KB)
CiphertextBlob	The encrypted output returned by KMS
fileb://	Prefix to specify binary file input for plaintext
Base64 decode	Required to convert KMS output to binary encrypted file

Key Takeaways

Use the AWS KMS Encrypt API with your key ID and plaintext to get encrypted data.

Always specify plaintext with the fileb:// prefix for binary data input.

Encrypted output is base64 encoded; decode it to store as binary.

KMS encrypts data up to 4 KB; use envelope encryption for larger data.

Ensure your IAM permissions allow use of the specified KMS key.