pretty Easy privacy (pEp): Privacy by Default
draft-birk-pep-01
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|
|
|---|---|---|---|
| Authors | Volker Birk , Hernâni Marques , S. Shelburn , Sandro Koechli | ||
| Last updated | 2018-01-09 | ||
| Replaced by | draft-pep-general | ||
| RFC stream | (None) | ||
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| Additional resources | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-birk-pep-01
Network Working Group V. Birk
Internet-Draft H. Marques
Intended status: Standards Track Shelburn
Expires: July 13, 2018 pEp Foundation
S. Koechli
pEp Security
January 09, 2018
pretty Easy privacy (pEp): Privacy by Default
draft-birk-pep-01
Abstract
Building on already available security formats and message transports
(like PGP/MIME for email), and with the intention to stay
interoperable to systems widespreadly deployed, pretty Easy privacy
(pEp) describes protocols to automatize operations (key management,
key discovery, private key handling including peer-to-peer
synchronization of private keys and other user data across devices)
that have been seen to be barriers to deployment of end-to-end secure
interpersonal messaging. pEp also introduces "Trustwords" (instead of
fingerprints) to verify communication peers and proposes a trust
rating system to denote secure types of communications and signal the
privacy level available on a per-user and per-message level. In this
document, the general design choices and principles of pEp are
outlined.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 13, 2018.
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Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
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to this document. Code Components extracted from this document must
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Protocol's core design principles . . . . . . . . . . . . . . 4
3.1. Compatibility . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Peer-to-Peer (P2P) . . . . . . . . . . . . . . . . . . . 4
3.3. User Experience (UX) . . . . . . . . . . . . . . . . . . 5
4. Identities in pEp . . . . . . . . . . . . . . . . . . . . . . 6
5. Key Management . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Private Keys . . . . . . . . . . . . . . . . . . . . . . 9
5.2. Key Distribution . . . . . . . . . . . . . . . . . . . . 10
5.3. Passphrases . . . . . . . . . . . . . . . . . . . . . . . 11
6. Privacy Status . . . . . . . . . . . . . . . . . . . . . . . 11
7. Options in pEp . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Option "Passive Mode" . . . . . . . . . . . . . . . . . . 12
7.2. Option "Disable Protection" . . . . . . . . . . . . . . . 12
7.2.1. For all communications . . . . . . . . . . . . . . . 12
7.2.2. For some communications . . . . . . . . . . . . . . . 12
7.3. Option "Extra Keys" . . . . . . . . . . . . . . . . . . . 12
7.4. Option "Blacklist Keys" . . . . . . . . . . . . . . . . . 13
7.5. Establishing trust between peers . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
9. Implementation Status . . . . . . . . . . . . . . . . . . . . 13
9.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 13
9.2. Reference implementation of pEp's core . . . . . . . . . 14
9.3. Abstract Crypto API examples . . . . . . . . . . . . . . 15
9.3.1. Encrypting a message . . . . . . . . . . . . . . . . 15
9.3.2. Decrypting a message . . . . . . . . . . . . . . . . 16
9.3.3. Obtaining common Trustwords . . . . . . . . . . . . . 17
9.4. Current software implementing pEp . . . . . . . . . . . . 18
10. Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
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12. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
12.1. Normative References . . . . . . . . . . . . . . . . . . 19
12.2. Informative References . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
[[At this stage it is not year clear to us how many of our
implementation details should be part of new RFCs and at which places
we can safely refer to already existing RFCs to make clear on which
RFCs we are already relying.]]
The pretty Easy privacy (pEp) protocols are propositions to the
Internet community to create software for peers to automatically
encrypt, anonymize (where possible, depending on the message
transport used) and verify their daily written digital communications
-- this is done by building upon already existing standards and tools
and automatizing all steps a user would need to carry out to engage
in secure end-to-end encrypted communciations without depending on
centralized infrastructures.
To mitigiate for Man-In-The-Middle Attacks (MITM) and as the only
manual step users may carry out, Trustwords as natural language
representations of two peers' fingerprints are proposed, for peers to
put trust on their communication channel.
Particularly, pEp proposes to automatize key management, key
discovery and also synchronization of secret key material by an in-
band peer-to-peer approach.
[[The pEp initiators had to learn from the CryptoParty movement, from
which the project emerged, that step-by-step guides can be helpful to
a particiular set of users to engage in secure end-to-end
communications, but that for a much major fraction of users it would
be more convenient to have the step-by-step procedures put into
actual code (as such, following a protocol) and thus automatizing the
initial configuration and whole usage of cryptographic tools.]]
The Privacy by Default principles that pretty Easy privacy (pEp)
introduces, are in accordance with the perspective outlined in
[RFC7435] to bring Opportunistic Security in the sense of "some
protection most of the time", with the subtle, but important
difference that when privacy is weighted against security, the choice
falls to privacy, which is why in pEp data minimization is a primary
goal (e.g., omitting unnecessary email headers or encrypting the
subject line).
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The pEp propositions are focused on written digital communications,
but not limited to asynchronous (offline) types of communications
like email, but can also be implemented for message transports, which
support synchronous (online) communications (e.g., for peer-to-peer
networks like GNUnet). pEp's goal is to bridge the different
standardized and/or widely spread communications channels, such that
users can reach their peers in the most privacy-enhancing way
possible using differing IRIs/URIs.
2. Terms
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Terms like "TOFU" or "MITM" are used as defined in [RFC4949].
o Handshake: The process when Alice -- e.g. in-person or via phone
-- contacts Bob to verifiy Trustwords (or by fallback:
fingerprints) is called handshake.
o Trustwords: A scalar-to-word representation of 16-bit numbers (0
to 65535) to natural language words. When doing a handshake,
peers are shown combined Trustwords of both public keys involved
to ease the comparison. [pEpTrustwords]
3. Protocol's core design principles
3.1. Compatibility
o Be conservative (strict) in requirements for pEp implementations
and how they behave between each other.
o Be liberal (accepting) in what comes in from non-pEp
implementations (e.g., do not send, but support to decipher PGP/
INLINE formats).
o Where pEp requires diverging from an RFC for privacy reasons
(e.g., from OpenPGP propositions as defined in [RFC4880]), options
SHOULD be implemented to empower the user to comply to practices
already (widespreadly) used, either at contact level or globally.
3.2. Peer-to-Peer (P2P)
All communications and verifications in pEp implementations for
pursuing secure and establishing trusted communications between peers
MUST be Peer-to-Peer (P2P) in nature.
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This means, there SHALL NOT be any pEp-specific central services
whatsoever needed for implementers of pEp to rely on, neither for
verification of peers nor for the actual encryption.
Still, implementers of pEp MAY provide options to interoperate with
providers of centralized infrastructures as users MAY NOT be stopped
from being able to communicate with their peers on platforms with
vendor lock-in.
Trust provided by global Certificate Authorities (e.g., commercial
X.509 CAs) SHALL NOT be signaled (cf. [pEpTrustRating]) as
trustworthy to users of pEp (e.g., when interoperating with peers
using S/MIME) by default.
3.3. User Experience (UX)
[[We are aware of the fact that usually UX requirements are not part
of RFCs. However, to have massively more people engaged in secure
end-to-end encryption and at the same time to avoid putting users at
risk, we believe requiring certain straightforward signaling for the
users to be a good idea -- in a similar way as this happens to be the
case for already popular Instant Messaging services.]]
Implementers of pEp MUST take special care to not confuse users with
t echnical terms, especially those of cryptography (e.g., "keys",
"certificates" or "fingerprints") if they do not explicitly ask for
them. Advanced settings MAY be available, in some cases further
options MUST be available, but they SHALL NOT be unnecessarily
exposed to users of pEp implementations at the first sight when using
clients implementing the pEp propositions.
The authors believe widespread adoption of end-to-end cryptography is
much less of an issue if the users are not hassled and visibly forced
in any way to use cryptography. That is, if they can just rely on
the principles of Privacy by Default.
By consequence, this means that users MUST NOT wait for cryptographic
tasks (e.g., key generation or public key retrieval) to finish before
being able to have their respective message clients ready to
communicate. This finally means, pEp implementers MUST make sure
that the ability to draft, send and receive messages is always
preserved -- even if that means a message is sent out unencrypted,
thus being in accordance with the Opportunistic Security approach
outlined in [RFC7435].
In turn, pEp implementers MUST make sure a Privacy Status is clearly
visible to the user on both contact and message level, such that
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users easily understand with what level of privacy messages are about
to be sent or were received, respectively.
4. Identities in pEp
With pEp users MUST have the possibility to have different
identities, which MUST not correlate to each other by default. On
the other hand, binding of different identities MUST be supported
(being for support of aliases).
[[This is the reason why in current pEp implementations for each
email account a different key pair is created, which allows a user to
retain different identities.]]
In particular, with pEp users MUST NOT be bound to a specific IRI/
URI, but SHALL be free to choose which identity they want to expose
to certain peers -- this includes support for pseudonymity and
anonymity, which the authors consider to be vital for users to
control their privacy.
[[It might be necessary to introduce further addressing schemes
through IETF contributions or IANA registrations.]]
In the reference implementation of the pEp Engine (cf. src/
pEpEngine.h), a pEp identity is defined like the following (C99):
typedef struct _pEp_identity {
char *address; // C string with address UTF-8 encoded
char *fpr; // C string with fingerprint UTF-8 encoded
char *user_id; // C string with user ID UTF-8 encoded
char *username; // C string with user name UTF-8 encoded
PEP_comm_type comm_type; // type of communication with this ID
char lang[3]; // language of conversation
// ISO 639-1 ALPHA-2, last byte is 0
bool me; // if this is the local user herself/himself
identity_flags_t flags; // identity_flag1 | identity_flag2 | ...
} pEp_identity;
A relational example (in SQL) used in current pEp implementations:
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CREATE TABLE pgp_keypair (
fpr text primary key,
created integer,
expires integer,
comment text,
flags integer default 0
);
CREATE TABLE person (
id text primary key,
username text not null,
main_key_id text
references pgp_keypair (fpr)
on delete set null,
lang text,
comment text,
device_group text
);
CREATE TABLE identity (
address text,
user_id text
references person (id)
on delete cascade,
main_key_id text
references pgp_keypair (fpr)
on delete set null,
comment text,
flags integer default 0, primary key (address, user_id)
);
The public key's fingerprint (denoted as fpr) as part of a pEp
identity MUST always be the full fingerprint.
Notable differences of how terms and concepts used differ between pEp
and OpenPGP:
+--------------------+--------------+-------------------------------+
| pEp | OpenPGP | Comments |
+--------------------+--------------+-------------------------------+
| user_id | (no concept) | ID for a person, i.e. a |
| | | contact |
| username + address | uid | comparable only for email |
| fpr | fingerprint | used as key ID in pEp |
| (no concept) | Key ID | does not exist in pEp |
+--------------------+--------------+-------------------------------+
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5. Key Management
Key management in pEp MUST be automatized in order to achieve the
goal of widespread adoption of secure communications.
A pEp implementation MUST make sure cryptographic keys for end-to-end
cryptography are generated for every identity configured (or
instantly upon its configuration) if no secure cryptographic setup
can be found. Users SHALL NOT be stopped from communicating -- this
also applies for initial situations where cryptographic keys are not
generated fast enough. This process MUST be carried out in the
background so the user is not stopped from communicating.
There is the pEp Trust Rating system in [pEpTrustRating] describing
which kind of encryption MUST be considered reliable and is thus
secure enough for usage in pEp implementations. This also applies
for keys already available for the given identity. If the available
keys are considered unsecure (e.g, insufficent key length), pEp
implementers are REQUIRED to generate new keys for use with the
respective identity.
As example for the rating of communication types, the definition of
the data structure by the pEp Engine reference implementation (cf.
src/pEpEngine.h) is provided:
typedef enum _PEP_comm_type {
PEP_ct_unknown = 0,
// range 0x01 to 0x09: no encryption, 0x0a to 0x0e: nothing reasonable
PEP_ct_no_encryption = 0x01, // generic
PEP_ct_no_encrypted_channel = 0x02,
PEP_ct_key_not_found = 0x03,
PEP_ct_key_expired = 0x04,
PEP_ct_key_revoked = 0x05,
PEP_ct_key_b0rken = 0x06,
PEP_ct_my_key_not_included = 0x09,
PEP_ct_security_by_obscurity = 0x0a,
PEP_ct_b0rken_crypto = 0x0b,
PEP_ct_key_too_short = 0x0c,
PEP_ct_compromized = 0x0e, // known compromized connection
PEP_ct_mistrusted = 0x0f, // known mistrusted key
// range 0x10 to 0x3f: unconfirmed encryption
PEP_ct_unconfirmed_encryption = 0x10, // generic
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PEP_ct_OpenPGP_weak_unconfirmed = 0x11, // RSA 1024 is weak
PEP_ct_to_be_checked = 0x20, // generic
PEP_ct_SMIME_unconfirmed = 0x21,
PEP_ct_CMS_unconfirmed = 0x22,
PEP_ct_strong_but_unconfirmed = 0x30, // generic
PEP_ct_OpenPGP_unconfirmed = 0x38, // key at least 2048 bit RSA or EC
PEP_ct_OTR_unconfirmed = 0x3a,
// range 0x40 to 0x7f: unconfirmed encryption and anonymization
PEP_ct_unconfirmed_enc_anon = 0x40, // generic
PEP_ct_pEp_unconfirmed = 0x7f,
PEP_ct_confirmed = 0x80, // this bit decides if trust is confirmed
// range 0x81 to 0x8f: reserved
// range 0x90 to 0xbf: confirmed encryption
PEP_ct_confirmed_encryption = 0x90, // generic
PEP_ct_OpenPGP_weak = 0x91, // RSA 1024 is weak (unused)
PEP_ct_to_be_checked_confirmed = 0xa0, //generic
PEP_ct_SMIME = 0xa1,
PEP_ct_CMS = 0xa2,
PEP_ct_strong_encryption = 0xb0, // generic
PEP_ct_OpenPGP = 0xb8, // key at least 2048 bit RSA or EC
PEP_ct_OTR = 0xba,
// range 0xc0 to 0xff: confirmed encryption and anonymization
PEP_ct_confirmed_enc_anon = 0xc0, // generic
PEP_ct_pEp = 0xff
} PEP_comm_type;
5.1. Private Keys
Private keys in pEp implementations MUST always be held on the end
user's device(s): pEp implementers SHALL NOT rely on private keys
stored in centralized remote locations. This also applies for key
storages where the private keys are protected with sufficiently long
passphrases. It MUST be considered a violation of pEp's P2P design
principle to rely on centralized infrastructures. This also applies
for pEp implementations created for applications not residing on a
user's device (e.g., web-based MUAs). In such cases, pEp
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implementations MUST be done in a way the locally-held private key
can neither be directly accessed nor leaked to the outside world.
[[It is particularly important that browser add-ons implementing pEp
functionality do not obtain their cryptographic code from a
centralized (cloud) service, as this must be considered a centralized
attack vector allowing for backdoors, negatively impacting privacy.]]
As a decentralized proposition, there is a pEp Key Synchronization
protocol. [pEpKeySync] It outlines how pEp implementers can
distribute their private keys in a secure and trusted manner: this
allows Internet users to read their messages across their different
devices, when sharing a common address (e.g., the same email
account).
5.2. Key Distribution
Implementers of pEp are REQUIRED to attach the identity's public key
to any outgoing message. However, this MAY be ommitted if you
previously received a message encrypted with the public key of the
receiver.
The sender's public key MUST be sent encrypted whenever possible,
i.e. when a public key of the receiving peer is available.
If no encryption key is available for the recipient, the sender's
public key MUST be sent unencrypted. In either case, this approach
ensures that message clients (e.g., MUAs which at least implement
OpenPGP) do not need to have pEp implemented to see a user's public
key. Such peers thus have the chance to (automatically) import the
sender's public key.
If there is already a known public key from the sender of a message
and it is still valid and not expired, new keys SHALL not be used for
future communication to avoid a MITM attack unless they are signed by
the previous key. Messages SHALL always be encrypted with the
receiving peer's oldest public key, as long as it is valid and not
expired.
Implementers of pEp SHALL make sure that public keys attached to
messages (e.g, in email) are not displayed to the user. This
ensures, they do not get confused by a file they cannot potentially
deal with.
Metadata (e.g., email headers) SHALL NOT be made to announce a user's
public key by the Privacy by Default principles. This must be
considered unnecessary information leakage, potentially affecting
privacy -- also depending on a country's data retention laws.
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Furtherly, this affects interoperability to existing users (e.g., in
the OpenPGP field) which have no notion of such header fields and
thus lose the ability to import any such keys distributed this way.
It SHOULD, though, be supported to obtain other users' public keys by
extracting them from respective header fields, in case such
approaches get widespread.
Keyservers or generally intermediate approaches to obtain a peer's
public key SHALL NOT be used by default. On the other hand, the user
MAY be given the option to opt-in for remote locations to obtain
keys, considering the widespread adoption of such approaches for key
distribution.
Keys generated or obtained by implementations SHALL NOT be uploaded
to any (intermediate) keystore locations without the user's explicit
will.
5.3. Passphrases
Passphrases to protect an user's private key MUST be supported by pEp
implementations, but SHALL NOT be enforced by default. That is, if a
pEp implementation finds a suitable (i.e., secure enough)
crytographic setup, which uses passphrases, pEp implementations MUST
provide a way to unlock the key. However, if a new key pair is
generated for a given identity no passphrase SHALL be put in place.
The authors assume that the enforcement of secure (i.e., unique and
long enough) passphrases would massively reduce the users of pEp (by
hassling them) -- and in turn provide little to no additional privacy
for the common cases of passive monitoring being carried out by
corporations and state-level actors.
6. Privacy Status
For end-users, the most important component of pEp, which MUST be
made visible on a per-recipient and per-message level, is the Privacy
Status.
By colors, symbols and texts a user SHALL immediately understand how
private
o a communication channel with a given peer was or ought to be and
o a given message was or ought to be.
The Privacy Status in its most general form MUST be expressed with
traffic lights semantics (and respective symbols and texts), whereas
the three colors yellow, green and red can be applied for any peer or
message -- like this immediately indicating how secure and
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trustworthy (and thus private) a communication was or ought to be
considered. In cases no (special) Privacy Status can be inferred for
peers or messages, no color (or the gray color) MUST be shown and
respective texts -- being "unknown" or "unreliable" -- MUST be shown.
The detailed Privacy Status as an end-user element of the pEp Trust
Rating system with all its states and respective represenations to be
followed is outlined in [pEpTrustRating].
7. Options in pEp
[[Just a selection; not yet complete.]]
7.1. Option "Passive Mode"
For situations where it might not be desirable to attach the sender's
public key for outgoing messages (which is the default), a "Passive
Mode" option MUST be made availble to avoid this.
7.2. Option "Disable Protection"
7.2.1. For all communications
Implementers of pEp MUST provide an option "Disable Protection" for
the user's will to disable any outgoing encryption and signing. This
option SHALL not affect the user's ability to decipher already
received or sent messages.
7.2.2. For some communications
For users to disable protection for some situations, i.e. at contact
or message level, pEp implementers MUST provide an option. This
allows users to disable outgoing encryption and signing for peers or
individual messages.
7.3. Option "Extra Keys"
For environments where there is the need to send messages to further
locations, pEp implementers MAY provide an "Extra Keys" option where
further recipients (by public key) can be specified. With the user's
will, each outgoing message MUST then be sent encrypted to any of
those extra (implicit) recipients. Message clients SHOULD save and
show only one message as sent to the explicit recipient(s), so as to
not confuse users.
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7.4. Option "Blacklist Keys"
An option "Blacklist Keys" MUST be provided for an advanced user to
be able to disable keys which the user does not want to be used
anymore for any new communications. However, the keys SHALL NOT be
deleted. It MUST still be possible to verify and decipher past
communications.
7.5. Establishing trust between peers
In pEp, Trustwords [pEpTrustwords] are used for users to compare the
authenticity of peers in order to mitigate for MITM attacks.
By default, Trustwords MUST be used to represent two peers'
fingerprints of their public keys in pEp implementations.
In order to retain compatibility with peers not using pEp
implementations (e.g., Mail User Agents (MUAs) with OpenPGP
implementations without Trustwords), it is REQUIRED that pEp
implementers give the user the choice to show both peers'
fingerprints instead of just their common Trustwords.
8. Security Considerations
By attaching the sender's public key to outgoing messages, Trust on
First Use (TOFU) is established, which can lead for MITM attacks to
succeed. Cryptographic key subversion is considered Pervasive
Monitoring (PM) according to [RFC7258]. Those attacks can be
mitigated by having the involved users comparing their common
Trustwords. This possibility MUST be made easily accessible to pEp
users in the user interface implementation. If for compatibility
reasons (e.g., with OpenPGP users) no Trustwords can be used, then an
comparibly easy way to verify the respective public key fingerprints
MUST be implemented.
Devices themselves SHOULD be made encrypted, as the use of
passphrases for private keys is not advised.
9. Implementation Status
9.1. Introduction
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
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here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
9.2. Reference implementation of pEp's core
The pEp Foundation provides a reference implementation of pEp's core
principles and functionalities, which go beyond the documentation
status of this Internet-Draft. [pEpCore]
pEp's reference implementation is composed of pEp Engine and pEp
Adapters (or bindings), alongside with some libraries which pEp
Engine relies on to function on certain platforms (like a NetPGP fork
we maintain for the iOS platform).
The pEp engine is a Free Software library encapsulating
implementations of:
o Key Management
* Key Management in pEp engine is based on GnuPG key chains
(NetPGP on iOS). Keys are stored in an OpenPGP compatbile
format and can be used for different crypto implementations.
o Trust Rating
* pEp engine is sporting a two phase trust rating system. In
phase one there is a rating based on channel, crypto and key
security named "comm_types". In phase 2 these are mapped to
user representable values which have attached colors to present
them in traffic light semantics.
o Abstract Crypto API
* The Abstract Crypto API is providing functions to encrypt and
decrypt data or full messages without requiring an application
programmer to understand the different formats and standards.
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o Message Transports
* pEp engine will support a growing list of Message Transports to
support any widespread text messaging system including email,
SMS, XMPP and many more.
pEp engine is written in C99. It is not meant to be used in
application code directly. Instead, pEp engine is coming together
with a list of software adapters for a variety of programming
languages and development environments, which are:
o pEp COM Server Adapter
o pEp JNI Adapter
o pEp JSON Adapter
o pEp ObjC (and Swift) Adapter
o pEp Python Adapter
o pEp Qt Adapter
9.3. Abstract Crypto API examples
[[Just a selection; more functionality available.]]
The following code excerpts are from the pEp Engine reference
implementation, to be found in src/message_api.h.
9.3.1. Encrypting a message
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// encrypt_message() - encrypt message in memory
//
// parameters:
// session (in) session handle
// src (in) message to encrypt
// extra (in) extra keys for encryption
// dst (out) pointer to new encrypted message or NULL on failure
// enc_format (in) encrypted format
// flags (in) flags to set special encryption features
//
// return value:
// PEP_STATUS_OK on success
// PEP_KEY_NOT_FOUND at least one of the receipient keys
// could not be found
// PEP_KEY_HAS_AMBIG_NAME at least one of the receipient keys has
// an ambiguous name
// PEP_GET_KEY_FAILED cannot retrieve key
// PEP_UNENCRYPTED no recipients with usable key,
// message is left unencrypted,
// and key is attached to it
//
// caveat:
// the ownershop of src remains with the caller
// the ownership of dst goes to the caller
DYNAMIC_API PEP_STATUS encrypt_message(
PEP_SESSION session,
message *src,
stringlist_t *extra,
message **dst,
PEP_enc_format enc_format,
PEP_encrypt_flags_t flags
);
9.3.2. Decrypting a message
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// decrypt_message() - decrypt message in memory
//
// parameters:
// session (in) session handle
// src (in) message to decrypt
// dst (out) pointer to new decrypted message or NULL on failure
// keylist (out) stringlist with keyids
// rating (out) rating for the message
// flags (out) flags to signal special decryption features
//
// return value:
// error status
// or PEP_DECRYPTED if message decrypted but not verified
// or PEP_STATUS_OK on success
//
// caveat:
// the ownership of src remains with the caller
// the ownership of dst goes to the caller
// the ownership of keylist goes to the caller
// if src is unencrypted this function returns PEP_UNENCRYPTED and sets
// dst to NULL
DYNAMIC_API PEP_STATUS decrypt_message(
PEP_SESSION session,
message *src,
message **dst,
stringlist_t **keylist,
PEP_rating *rating,
PEP_decrypt_flags_t *flags
);
9.3.3. Obtaining common Trustwords
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// get_trustwords() - get full trustwords string for a *pair* of identities
//
// parameters:
// session (in) session handle
// id1 (in) identity of first party in communication - fpr can't be NULL
// id2 (in) identity of second party in communication - fpr can't be NULL
// lang (in) C string with ISO 639-1 language code
// words (out) pointer to C string with all trustwords UTF-8 encoded,
// separated by a blank each
// NULL if language is not supported or trustword
// wordlist is damaged or unavailable
// wsize (out) length of full trustwords string
// full (in) if true, generate ALL trustwords for these identities.
// else, generate a fixed-size subset. (TODO: fixed-minimum-entropy
// subset in next version)
//
// return value:
// PEP_STATUS_OK trustwords retrieved
// PEP_OUT_OF_MEMORY out of memory
// PEP_TRUSTWORD_NOT_FOUND at least one trustword not found
//
// caveat:
// the word pointer goes to the ownership of the caller
// the caller is responsible to free() it (on Windoze use pEp_free())
//
DYNAMIC_API PEP_STATUS get_trustwords(
PEP_SESSION session, const pEp_identity* id1, const pEp_identity* id2,
const char* lang, char **words, size_t *wsize, bool full
);
9.4. Current software implementing pEp
The following software implementing the pEp protocols (to varying
degrees) already exists; it does not yet go beyond implementing pEp
for email, which is to be described nearer in [pEpEmail]:
o pEp for Outlook as addon for Microsoft Outlook, production
[pEpForOutlookSrc]
o pEp for Android (based on a fork of the K9 MUA), beta
[pEpForAndroidSrc]
o Enigmail/pEp as addon for Mozilla Thunderbird, early beta
[EnigmailpEpSrc]
o pEp for iOS (implemented in a new MUA), alpha [pEpForiOSSrc]
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pEp for Android, iOS and Outlook are provided by pEp Security, a
commercial entity specializing in end-user software implementing pEp
while Enigmail/pEp is pursued as community project, supported by the
pEp Foundation.
10. Notes
The pEp logo and "pretty Easy privacy" are registered trademarks
owned by pEp Foundation in Switzerland, a tax-free, non-commercial
entity.
Primarily, we want to ensure the following:
o Software using the trademarks MUST be backdoor-free.
o Software using the trademarks MUST be accompanied by a serious
(detailed) code audit carried out by a reputable third-party, for
any proper release.
The pEp Foundation will help to support any community-run (non-
commercial) project with the latter, be it organizationally or
financially.
Through this, the foundation wants to make sure that software using
the pEp trademarks is as safe as possible from a security and privacy
point of view.
11. Acknowledgements
Special thanks to Bernie Hoeneisen, Enrico Tomae, Stephen Farrel,
Brian Trammell and Neal Walfield for roughly reviewing first versions
of this Internet-Draft and providing valuable feedback and patches.
[[Much more general acknowledgements to follow.]]
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4880] Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R.
Thayer, "OpenPGP Message Format", RFC 4880,
DOI 10.17487/RFC4880, November 2007,
<https://www.rfc-editor.org/info/rfc4880>.
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[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>.
[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
December 2014, <https://www.rfc-editor.org/info/rfc7435>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
12.2. Informative References
[EnigmailpEpSrc]
Enigmail project, "Source code for Enigmail/pEp", June
2017,
<https://enigmail.net/index.php/en/download/source-code>.
[pEpCore] pEp Foundation, "Core source code and reference
implementation of pEp (engine and adapters)", June 2017,
<https://letsencrypt.pep.foundation/dev/>.
[pEpEmail]
pEp Foundation, "pEp email [Early Internet-Draft]", June
2017, <https://letsencrypt.pep.foundation/trac/browser/
internet-drafts/pep-email/draft-birk-pep-email-NN.txt>.
[pEpForAndroidSrc]
pEp Security, "Source code for pEp for Android", June
2017, <https://cacert.pep-security.lu/gitlab/android/pep>.
[pEpForiOSSrc]
pEp Security, "Source code for pEp for iOS", June 2017,
<https://cacert.pep-security.ch/dev/repos/pEp_for_iOS/>.
[pEpForOutlookSrc]
pEp Security, "Source code for pEp for Outlook", June
2017, <https://cacert.pep-security.lu/dev/repos/
pEp_for_Outlook/>.
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[pEpKeySync]
pEp Foundation, "pEp Key Synchronization Protocol [Early
Internet-Draft]", June 2017,
<https://letsencrypt.pep.foundation/trac/browser/internet-
drafts/pep-keysync/draft-birk-pep-keysync-NN.txt>.
[pEpTrustRating]
pEp Foundation, "pretty Easy privacy (pEp): Trust Rating
System [Early Internet-Draft]", June 2017,
<https://letsencrypt.pep.foundation/trac/browser/internet-
drafts/pep-rating/draft-birk-pep-rating-NN.txt>.
[pEpTrustwords]
pEp Foundation, "pretty Easy privacy (pEp): Trustwords
concept [Early Internet-Draft]", June 2017,
<https://letsencrypt.pep.foundation/trac/browser/internet-
drafts/pep-trustwords/draft-birk-pep-trustwords-NN.txt>.
Authors' Addresses
Volker Birk
pEp Foundation
Email: vb@pep-project.org
Hernani Marques
pEp Foundation
Email: hernani.marques@pep.foundation
Shelburn
pEp Foundation
Email: shelburn@pep.foundation
Sandro Koechli
pEp Security
Email: sandro@pep-security.net
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