IAM policy can be used to give readonly access to a single S3 bucket in Amazon cloud for a particular user.

	{
  "Statement": [
    {
      "Action": [
        "s3:GetBucketAcl",
        "s3:GetBucketLocation",
        "s3:GetBucketNotification",
        "s3:GetBucketPolicy",
        "s3:GetBucketRequestPayment",
        "s3:GetBucketVersioning",
        "s3:GetObject",
        "s3:GetObjectAcl",
        "s3:GetObjectVersion",
        "s3:GetObjectVersionAcl",
        "s3:ListBucket",
        "s3:ListBucketMultipartUploads",
        "s3:ListBucketVersions",
        "s3:ListMultipartUploadParts"
      ],
      "Effect": "Allow",
      "Resource": [
        "arn:aws:s3:::BUCKET_NAME",
        "arn:aws:s3:::BUCKET_NAME/*"
      ]
    }
  ]
}