credstash.py

#!/usr/bin/env python
# Copyright 2015 Luminal, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import argparse
import boto.dynamodb2
import boto.kms
import csv
import json
import operator
import os
import os.path
import StringIO
import sys
import time
import re

try:
    import yaml
    NO_YAML = False
except ImportError:
    NO_YAML = True

from base64 import b64encode, b64decode
from boto.dynamodb2.exceptions import ConditionalCheckFailedException
from boto.dynamodb2.exceptions import ItemNotFound
from boto.dynamodb2.fields import HashKey, RangeKey
from boto.dynamodb2.table import Table
from boto.dynamodb2.types import STRING
from Crypto.Cipher import AES
from Crypto.Hash import SHA256
from Crypto.Hash.HMAC import HMAC
from Crypto.Util import Counter

DEFAULT_REGION = "us-east-1"
WILDCARD_CHAR = "*"


class KmsError(Exception):
    def __init__(self, value=""):
        self.value = "KMS ERROR: " + value if value is not "" else "KMS ERROR"

    def __str__(self):
        return self.value


class IntegrityError(Exception):
    def __init__(self, value=""):
        self.value = "INTEGRITY ERROR: " + value if value is not "" else \
                     "INTEGRITY ERROR"

    def __str__(self):
        return self.value


class KeyValueToDictionary(argparse.Action):
    def __call__(self, parser, namespace, values, option_string=None):
        setattr(namespace,
                self.dest,
                dict((x[0], x[1]) for x in values))


def printStdErr(s):
    sys.stderr.write(str(s))
    sys.stderr.write("\n")


def key_value_pair(string):
    output = string.split('=')
    if len(output) != 2:
        msg = "%r is not the form of \"key=value\"" % string
        raise argparse.ArgumentTypeError(msg)
    return output


def expand_wildcard(string, secrets):
    prog = re.compile('^' + string.replace(WILDCARD_CHAR, '.*') + '$')
    output = []
    for secret in secrets:
        if prog.search(secret) is not None:
            output.append(secret)
    return output


def value_or_filename(string):
    if string[0] == "@":
        filename = string[1:]
        try:
            with open(os.path.expanduser(filename)) as f:
                output = f.read()
        except IOError as e:
            raise argparse.ArgumentTypeError("Unable to read file %s" %
                                             filename)
    else:
        output = string
    return output


def csv_dump(dictionary):
    csvfile = StringIO.StringIO()
    csvwriter = csv.writer(csvfile)
    for key in dictionary:
        csvwriter.writerow([key, dictionary[key]])
    return csvfile.getvalue()


def getHighestVersion(name, region="us-east-1", table="credential-store"):
    '''
    Return the highest version of `name` in the table
    '''
    secretStore = Table(table,
                        connection=boto.dynamodb2.connect_to_region(region))
    result_set = [x for x in secretStore.query_2(limit=1, reverse=True,
                                                 consistent=True,
                                                 name__eq=name)]
    if not result_set:
        return 0
    else:
        return result_set[0]["version"]


def listSecrets(region="us-east-1", table="credential-store"):
    '''
    do a full-table scan of the credential-store,
    and return the names and versions of every credential
    '''
    secretStore = Table(table,
                        connection=boto.dynamodb2.connect_to_region(region))
    rs = secretStore.scan(attributes=("name", "version"))
    return [secret for secret in rs]


def putSecret(name, secret, version, kms_key="alias/credstash",
              region="us-east-1", table="credential-store", context=None):
    '''
    put a secret called `name` into the secret-store,
    protected by the key kms_key
    '''
    kms = boto.kms.connect_to_region(region)
    # generate a a 64 byte key.
    # Half will be for data encryption, the other half for HMAC
    try:
        kms_response = kms.generate_data_key(kms_key, context, 64)
    except:
        raise KmsError("Could not generate key using KMS key %s" % kms_key)
    data_key = kms_response['Plaintext'][:32]
    hmac_key = kms_response['Plaintext'][32:]
    wrapped_key = kms_response['CiphertextBlob']

    enc_ctr = Counter.new(128)
    encryptor = AES.new(data_key, AES.MODE_CTR, counter=enc_ctr)

    c_text = encryptor.encrypt(secret)
    # compute an HMAC using the hmac key and the ciphertext
    hmac = HMAC(hmac_key, msg=c_text, digestmod=SHA256)
    b64hmac = hmac.hexdigest()

    secretStore = Table(table,
                        connection=boto.dynamodb2.connect_to_region(region))

    data = {}
    data['name'] = name
    data['version'] = version if version != "" else "1"
    data['key'] = b64encode(wrapped_key)
    data['contents'] = b64encode(c_text)
    data['hmac'] = b64hmac
    return secretStore.put_item(data=data)


def getAllSecrets(version="", region="us-east-1",
                  table="credential-store", context=None):
    '''
    fetch and decrypt all secrets
    '''
    output = {}
    secrets = listSecrets(region, table)
    for credential in set([x["name"] for x in secrets]):
        try:
            output[credential] = getSecret(credential,
                                           version,
                                           region,
                                           table,
                                           context)
        except:
            pass
    return output


def getSecret(name, version="", region="us-east-1",
              table="credential-store", context=None):
    '''
    fetch and decrypt the secret called `name`
    '''
    secretStore = Table(table,
                        connection=boto.dynamodb2.connect_to_region(region))
    if version == "":
        # do a consistent fetch of the credential with the highest version
        result_set = [x for x in secretStore.query_2(limit=1, reverse=True,
                                                     consistent=True,
                                                     name__eq=name)]
        if not result_set:
            raise ItemNotFound("Item {'name': '%s'} couldn't be found." % name)
        material = result_set[0]
    else:
        material = secretStore.get_item(name=name, version=version)

    kms = boto.kms.connect_to_region(region)
    # Check the HMAC before we decrypt to verify ciphertext integrity
    try:
        kms_response = kms.decrypt(b64decode(material['key']), context)
    except boto.kms.exceptions.InvalidCiphertextException:
        if context is None:
            msg = ("Could not decrypt hmac key with KMS. The credential may "
                   "require that an encryption context be provided to decrypt "
                   "it.")
        else:
            msg = ("Could not decrypt hmac key with KMS. The encryption "
                   "context provided may not match the one used when the "
                   "credential was stored.")
        raise KmsError(msg)
    except Exception as e:
        raise KmsError("Decryption error %s" % e)
    key = kms_response['Plaintext'][:32]
    hmac_key = kms_response['Plaintext'][32:]
    hmac = HMAC(hmac_key, msg=b64decode(material['contents']),
                digestmod=SHA256)
    if hmac.hexdigest() != material['hmac']:
        raise IntegrityError("Computed HMAC on %s does not match stored HMAC"
                             % name)
    dec_ctr = Counter.new(128)
    decryptor = AES.new(key, AES.MODE_CTR, counter=dec_ctr)
    plaintext = decryptor.decrypt(b64decode(material['contents']))
    return plaintext


def deleteSecrets(name, region="us-east-1", table="credential-store"):
    secretStore = Table(table,
                        connection=boto.dynamodb2.connect_to_region(region))
    rs = secretStore.scan(name__eq=name)
    for i in rs:
        print("Deleting %s -- version %s" % (i["name"], i["version"]))
        i.delete()


def createDdbTable(region="us-east-1", table="credential-store"):
    '''
    create the secret store table in DDB in the specified region
    '''
    d_conn = boto.dynamodb2.connect_to_region(region)
    if table in d_conn.list_tables()['TableNames']:
        print("Credential Store table already exists")
        return
    print("Creating table...")
    secrets = Table.create(table, schema=[
        HashKey('name', data_type=STRING),
        RangeKey('version', data_type=STRING)
        ], throughput={
            'read': 1,
            'write': 1
        }, connection=d_conn)
    timeout = 1
    while secrets.describe()['Table']['TableStatus'] != "ACTIVE":
        print("Waiting for table to be created...")
        time.sleep(timeout)
        timeout = timeout * 2 if timeout < 8 else timeout
    print("Table has been created. "
          "Go read the README about how to create your KMS key")


def main():
    parsers = {}
    parsers['super'] = argparse.ArgumentParser(
        description="A credential/secret storage system")

    parsers['super'].add_argument("-r", "--region",
                                  help="the AWS region in which to operate."
                                  "If a region is not specified, credstash "
                                  "will use the value of the "
                                  "AWS_DEFAULT_REGION env variable, "
                                  "or if that is not set, us-east-1")
    parsers['super'].add_argument("-t", "--table", default="credential-store",
                                  help="DynamoDB table to use for "
                                  "credential storage")
    subparsers = parsers['super'].add_subparsers(help='Try commands like '
                                                 '"{name} get -h" or "{name}'
                                                 'put --help" to get each'
                                                 'sub command\'s options'
                                                 .format(name=os.path.basename(
                                                         __file__)))

    action = 'delete'
    parsers[action] = subparsers.add_parser(action,
                                            help='Delete a credential " \
                                            "from the store')
    parsers[action].add_argument("credential", type=str,
                                 help="the name of the credential to delete")
    parsers[action].set_defaults(action=action)

    action = 'get'
    parsers[action] = subparsers.add_parser(action, help="Get a credential "
                                            "from the store")
    parsers[action].add_argument("credential", type=str,
                                 help="the name of the credential to get."
                                 "Using the wildcard character '%s' will "
                                 "search for credentials that match the "
                                 "pattern" % WILDCARD_CHAR)
    parsers[action].add_argument("context", type=key_value_pair,
                                 action=KeyValueToDictionary, nargs='*',
                                 help="encryption context key/value pairs "
                                 "associated with the credential in the form "
                                 "of \"key=value\"")
    parsers[action].add_argument("-n", "--noline", action="store_true",
                                 help="Don't append newline to returned "
                                 "value (useful in scripts or with "
                                 "binary files)")
    parsers[action].add_argument("-v", "--version", default="",
                                 help="Get a specific version of the "
                                 "credential (defaults to the latest version)")
    parsers[action].set_defaults(action=action)

    action = 'getall'
    parsers[action] = subparsers.add_parser(action,
                                            help="Get all credentials from "
                                            "the store")
    parsers[action].add_argument("context", type=key_value_pair,
                                 action=KeyValueToDictionary, nargs='*',
                                 help="encryption context key/value pairs "
                                 "associated with the credential in the form "
                                 "of \"key=value\"")
    parsers[action].add_argument("-v", "--version", default="",
                                 help="Get a specific version of the "
                                 "credential (defaults to the latest version)")
    parsers[action].add_argument("-f", "--format", default="json",
                                 choices=["json", "csv"] +
                                 ([] if NO_YAML else ["yaml"]),
                                 help="Output format. json(default) " +
                                 ("" if NO_YAML else "yaml ") + "or csv.")
    parsers[action].set_defaults(action=action)

    action = 'list'
    parsers[action] = subparsers.add_parser(action,
                                            help="list credentials and "
                                            "their versions")
    parsers[action].set_defaults(action=action)

    action = 'put'
    parsers[action] = subparsers.add_parser(action,
                                            help="Put a credential into "
                                            "the store")
    parsers[action].add_argument("credential", type=str,
                                 help="the name of the credential to store")
    parsers[action].add_argument("value", type=value_or_filename,
                                 help="the value of the credential to store "
                                 "or, if beginning with the \"@\" character, "
                                 "the filename of the file containing "
                                 "the value", default="")
    parsers[action].add_argument("context", type=key_value_pair,
                                 action=KeyValueToDictionary, nargs='*',
                                 help="encryption context key/value pairs "
                                 "associated with the credential in the form "
                                 "of \"key=value\"")
    parsers[action].add_argument("-k", "--key", default="alias/credstash",
                                 help="the KMS key-id of the master key "
                                 "to use. See the README for more "
                                 "information. Defaults to alias/credstash")
    parsers[action].add_argument("-v", "--version", default="",
                                 help="Put a specific version of the "
                                 "credential (update the credential; "
                                 "defaults to version `1`).")
    parsers[action].set_defaults(action=action)

    action = 'setup'
    parsers[action] = subparsers.add_parser(action,
                                            help='setup the credential store')
    parsers[action].set_defaults(action=action)

    args = parsers['super'].parse_args()
    region = os.getenv(
        "AWS_DEFAULT_REGION", DEFAULT_REGION) if not args.region \
        else args.region
    if args.action == "delete":
        deleteSecrets(args.credential, region=region, table=args.table)
        return
    if args.action == "list":
        credential_list = listSecrets(region=region, table=args.table)
        if credential_list:
            # print list of credential names and versions,
            # sorted by name and then by version
            max_len = max([len(x["name"]) for x in credential_list])
            for cred in sorted(credential_list,
                               key=operator.itemgetter("name", "version")):
                print("{0:{1}} -- version {2:>}".format(
                    cred["name"], max_len, cred["version"]))
        else:
            return
    if args.action == "put":
        try:
            if putSecret(args.credential, args.value, args.version,
                         kms_key=args.key, region=region, table=args.table,
                         context=args.context):
                print("{0} has been stored".format(args.credential))
        except KmsError as e:
            printStdErr(e)
        except ConditionalCheckFailedException:
            latestVersion = getHighestVersion(args.credential, region,
                                              args.table)
            printStdErr("%s version %s is already in the credential store. "
                        "Use the -v flag to specify a new version" %
                        (args.credential, latestVersion))
        return
    if args.action == "get":
        try:
            if WILDCARD_CHAR in args.credential:
                names = expand_wildcard(args.credential,
                                        [x["name"]
                                         for x
                                         in listSecrets(region=region,
                                                        table=args.table)])
                print(json.dumps(dict((name,
                                      getSecret(name,
                                                args.version,
                                                region=region,
                                                table=args.table,
                                                context=args.context))
                                      for name in names)))
            else:
                sys.stdout.write(getSecret(args.credential, args.version,
                                           region=region, table=args.table,
                                           context=args.context))
                if not args.noline:
                    sys.stdout.write("\n")
        except ItemNotFound as e:
            printStdErr(e)
        except KmsError as e:
            printStdErr(e)
        except IntegrityError as e:
            printStdErr(e)
        return
    if args.action == "getall":
        secrets = getAllSecrets(args.version,
                                region=region,
                                table=args.table,
                                context=args.context)
        if args.format == "json":
            output_func = json.dumps
            output_args = {"sort_keys": True,
                           "indent": 4,
                           "separators": (',', ': ')}
        elif not NO_YAML and args.format == "yaml":
            output_func = yaml.dump
            output_args = {"default_flow_style": False}
        elif args.format == 'csv':
            output_func = csv_dump
            output_args = {}
        print(output_func(secrets, **output_args))
        return
    if args.action == "setup":
        createDdbTable(region=region, table=args.table)
        return

if __name__ == '__main__':
    main()