カスタムキーを作成して、S3 バケットからファイルをダウンロードしようとしたが、失敗した。
どうやら、カスタムキーの key policy を変更しなければならないようだ。
以下は、AWS KMS の s3 用の managed policy。ここの、一部分をコピーして、作成した KMS の key policy に貼り付けて保存した。
{
"Version": "2012-10-17",
"Id": "auto-s3-2",
"Statement": [
{
"Sid": "Allow access through S3 for all principals in the account that are authorized to use S3",
"Effect": "Allow",
"Principal": {
"AWS": "*"
},
"Action": [
"kms:Encrypt",
"kms:Decrypt",
"kms:ReEncrypt*",
"kms:GenerateDataKey*",
"kms:DescribeKey"
],
"Resource": "*",
"Condition": {
"StringEquals": {
"kms:CallerAccount": "<ACCOUNT_ID>",
"kms:ViaService": "s3.<REGION>.amazonaws.com"
}
}
},
{
"Sid": "Allow direct access to key metadata to the account",
"Effect": "Allow",
"Principal": {
"AWS": "arn:aws:iam::<ACCOUNT_ID>:root"
},
"Action": [
"kms:Describe*",
"kms:Get*",
"kms:List*"
],
"Resource": "*"
}
]
}
KMS key を作成したばかりの key policy
{
"Version": "2012-10-17",
"Id": "key-consolepolicy-3",
"Statement": [
{
"Sid": "Enable IAM User Permissions",
"Effect": "Allow",
"Principal": {
"AWS": "arn:aws:iam::<ACCOUNT_ID>:root"
},
"Action": "kms:*",
"Resource": "*"
},
{
"Sid": "Allow access for Key Administrators",
"Effect": "Allow",
"Principal": {
"AWS": "arn:aws:iam::<ACCOUNT_ID>:user/<USER>"
},
"Action": [
"kms:Create*",
"kms:Describe*",
"kms:Enable*",
"kms:List*",
"kms:Put*",
"kms:Update*",
"kms:Revoke*",
"kms:Disable*",
"kms:Get*",
"kms:Delete*",
"kms:TagResource",
"kms:UntagResource",
"kms:ScheduleKeyDeletion",
"kms:CancelKeyDeletion"
],
"Resource": "*"
},
{
"Sid": "Allow use of the key",
"Effect": "Allow",
"Principal": {
"AWS": "arn:aws:iam::<ACCOUNT_ID>:user/<USER>"
},
"Action": [
"kms:Encrypt",
"kms:Decrypt",
"kms:ReEncrypt*",
"kms:GenerateDataKey*",
"kms:DescribeKey"
],
"Resource": "*"
},
{
"Sid": "Allow attachment of persistent resources",
"Effect": "Allow",
"Principal": {
"AWS": "arn:aws:iam::<ACCOUNT_ID>:user/<USER>"
},
"Action": [
"kms:CreateGrant",
"kms:ListGrants",
"kms:RevokeGrant"
],
"Resource": "*",
"Condition": {
"Bool": {
"kms:GrantIsForAWSResource": "true"
}
}
}
]
}
AWS の s3用の managed key policy の一部を貼り付けて完成させた key policy。
{
"Version": "2012-10-17",
"Id": "key-consolepolicy-3",
"Statement": [
{
"Sid": "Enable IAM User Permissions",
"Effect": "Allow",
"Principal": {
"AWS": "arn:aws:iam::<ACCOUNT_ID>:root"
},
"Action": "kms:*",
"Resource": "*"
},
{
"Sid": "Allow access for Key Administrators",
"Effect": "Allow",
"Principal": {
"AWS": "arn:aws:iam::<ACCOUNT_ID>:user/<USER>"
},
"Action": [
"kms:Create*",
"kms:Describe*",
"kms:Enable*",
"kms:List*",
"kms:Put*",
"kms:Update*",
"kms:Revoke*",
"kms:Disable*",
"kms:Get*",
"kms:Delete*",
"kms:TagResource",
"kms:UntagResource",
"kms:ScheduleKeyDeletion",
"kms:CancelKeyDeletion"
],
"Resource": "*"
},
{
"Sid": "Allow use of the key",
"Effect": "Allow",
"Principal": {
"AWS": "arn:aws:iam::<ACCOUNT_ID>:user/<USER>"
},
"Action": [
"kms:Encrypt",
"kms:Decrypt",
"kms:ReEncrypt*",
"kms:GenerateDataKey*",
"kms:DescribeKey"
],
"Resource": "*"
},
{
"Sid": "Allow attachment of persistent resources",
"Effect": "Allow",
"Principal": {
"AWS": "arn:aws:iam::<ACCOUNT_ID>:user/<USER>"
},
"Action": [
"kms:CreateGrant",
"kms:ListGrants",
"kms:RevokeGrant"
],
"Resource": "*",
"Condition": {
"Bool": {
"kms:GrantIsForAWSResource": "true"
}
}
},
{
"Sid": "Allow access through S3 for all principals in the account that are authorized to use S3",
"Effect": "Allow",
"Principal": {
"AWS": "*"
},
"Action": [
"kms:Encrypt",
"kms:Decrypt",
"kms:ReEncrypt*",
"kms:GenerateDataKey*",
"kms:DescribeKey"
],
"Resource": "*",
"Condition": {
"StringEquals": {
"kms:ViaService": "s3.<REGION>.amazonaws.com",
"kms:CallerAccount": "<ACCOUNT_ID>"
}
}
}
]
}
ダウンロードするためのコマンド
aws s3 cp s3://<BUCKET_NAME>/<OBJECT_NAME> . --sse aws:kms --sse-kms-key-id <CUSTOM_KEY_ID>
（参考リンク）
https://aws.amazon.com/jp/premiumsupport/knowledge-center/s3-object-encryption-keys/
https://docs.aws.amazon.com/kms/latest/developerguide/key-policies.html#key-policy-example