Use GetBucketEncryption with an AWS SDK or CLI

    /// <summary>
    /// Get and print the encryption settings of a bucket.
    /// </summary>
    /// <param name="bucketName">Name of the bucket.</param>
    /// <returns>Async task.</returns>
    public static async Task GetEncryptionSettings(string bucketName)
    {
        // Check and print the bucket encryption settings.
        Console.WriteLine($"Getting encryption settings for bucket {bucketName}.");

        try
        {
            var settings =
                await _s3Client.GetBucketEncryptionAsync(
                    new GetBucketEncryptionRequest() { BucketName = bucketName });

            foreach (var encryptionSettings in settings?.ServerSideEncryptionConfiguration?.ServerSideEncryptionRules!)
            {
                Console.WriteLine(
                    $"\tAlgorithm: {encryptionSettings.ServerSideEncryptionByDefault.ServerSideEncryptionAlgorithm}");
                Console.WriteLine(
                    $"\tKey: {encryptionSettings.ServerSideEncryptionByDefault.ServerSideEncryptionKeyManagementServiceKeyId}");
            }
        }
        catch (AmazonS3Exception ex)
        {
            Console.WriteLine(ex.ErrorCode == "InvalidBucketName"
                ? $"Bucket {bucketName} was not found."
                : $"Unable to get bucket encryption for bucket {bucketName}, {ex.Message}");
        }
    }

To retrieve the server-side encryption configuration for a bucket

The following get-bucket-encryption example retrieves the server-side encryption configuration for the bucket amzn-s3-demo-bucket.

aws s3api get-bucket-encryption \
    --bucket amzn-s3-demo-bucket

Output:

{
    "ServerSideEncryptionConfiguration": {
        "Rules": [
            {
                "ApplyServerSideEncryptionByDefault": {
                    "SSEAlgorithm": "AES256"
                }
            }
        ]
    }
}

Example 1: This command returns all the server side encryption rules associated with the given bucket.

Get-S3BucketEncryption -BucketName 'amzn-s3-demo-bucket'