The birth of electronic signature, public and private key cryptography, standardization, PKI and PGP architectures. Legal value of the electronic signature and main technical aspects.

1. 1
Digital Signature and Digital Identity
from RSA to eIDAS
Emanuele CIsbani
ecisbani@intesigroup.com
31-03-2021 - Università Milano Bicocca

2. 2
2
Agenda
● Beginning
● Standards
● Digital Identity
● Decentralization
● Tools

3. 3
Beginning

4. Symmetric Cryptography
Un uomo che non si interessa allo Stato
noi non lo consideriamo innocuo, ma
inutile; e benchè in pochi siano in grado
di dare vita ad una politica, beh tutti qui
ad Atene siamo in grado di giudicarla. Noi
non consideriamo la discussione come un
ostacolo sulla via della democrazia. Noi
crediamo che la felicità sia il frutto della
libertà, ma la libertà sia solo il frutto del
valore. Insomma, io proclamo che Atene
è la scuola dell’Ellade e che ogni ateniese
cresce sviluppando in sé una felice
versatilità, la fiducia in se stesso, la
prontezza a fronteggiare qualsiasi
situazione ed è per questo che la nostra
città è aperta al mondo e noi non
cacciamo mai uno straniero.
Qui ad Atene noi facciamo così.
4
https://www.tools4noobs.com/online_tools/encrypt/
xq2YkJdEv5VjHIAEdnrRO09ldohxnj8DjNjFX73rHKMtxqX6cA
I71TTPMILmCvRrh8yAwfLildPiy5XqXgdjQMg8VVer8k6oggiy
QeKLI3vv1vwykvJwl1FIX6K+LywlaOTsKN5cEIKP95+I+I9mnr
/lZuH+R2psdDs/bu6aw++3lYQq5/+Z55tuE49JZ+ABq7b71m+
F26BFn9jPYyxtFekUqOqDtLwJ4lyIFFK+qbTPpL/AEDrdQaee
Gp7PINvc0Ejnhht8LjHGiAGenCoWud2FfhXEsJTT8+42VBs
m1k3kN+CQ6wu9j2e2Bqr0UbhR6WJgadVk51Z21zBpBkLo1
Uc+veEUP6XDCzZBN/9D3HarJp6t+kLfOKOCjBBPxdIoYPkR
qBWT9Pcm4bP0JDVBMUnmakSlpbndz+zXSaQZRVPwHuI1
dWtPW4ZPWhsevjQBrITKEnPszYuNTkb/Ouxb6qMr+NyX1G
V5AQ+npMu+Lj5/QevpH99amyj8+caNrjdTUlOB0y5r/luQaF4
8xExenOc+8jn9vUJn3v5BX26hp9IEr4lnNMimmarH8H1V5Ov
Wy6rSFxsr74tyZnmw4Il7TTcsTeLiLPs+7qqapTsZHejSVJB1x
Y+5qWutvyzIYfSq2nuNHRPuwkdDC9VZPureEGwYi0pkdgfU
DVm3RQLoWmrm8IayItFVcPxEHHHTce7pec4Y4+IktHQlJX
SMrfbGFugRo/iAjy/+dp3rV0wFqsj6YGwlyWjWw0n1KXYHOG
jIyWMbXG+2CxTI4qKRGI3kayz8HO0rHkNYZ9LgxnqTvKbQ
Nvcd3g9u/r53q/wJ7WkGYjeRdlHvHSCLwFXdbUoja2Q+AjZu
CXYI/vyASrgANh3wPNabnMhu5HpKkTkOuHfExsZPKHes7n
6GtqasQR5QiZ/evq613Os9BpXM2/WvCQn3773LdSrV2bqY
Ac6g5SZe
Pericle
DES-CBC
Base64

5. Symmetric Cryptography
In symmetric encryption, the
recipient of the encrypted
message must have the same
key used by the sender who
encrypted it
This requires that the sender
and recipient previously have a
secure channel through which
to exchange the key
5

6. 6
6-11-1976, New Directions in Cryptography
Abstract - Two kinds of contemporary
developments in cryptography are examined.
Widening applications of teleprocessing have
given rise to a need for new types of
cryptographic systems, which minimize the need
for secure key distribution channels and supply
the equivalent of a written signature. This
paper suggests ways to solve these currently
open problems. It also discusses how the
theories of communication and computation are
beginning to provide the tools to solve
cryptographic problems of long standing.
Whitfield Diffie
5-6-1944
Prophet of Privacy
Martin Hellman
1-10-1945
https://ee.stanford.edu/~hellman/publications/24.pdf
https://cacm.acm.org/magazines/2016/6/202666-qa-finding-new-directions-in-cryptography/fulltext
https://www.wired.com/1994/11/diffie/

7. 7
Secure communication over an insecure channel
The system...has since become known as
Diffie–Hellman key exchange. While that
system was first described in a paper by Diffie
and me, it is a public key distribution system, a
concept developed by Merkle, and hence
should be called 'Diffie–Hellman–Merkle key
exchange' if names are to be associated with it.
I hope this small pulpit might help in that
endeavor to recognize Merkle's equal
contribution to the invention of public key
cryptography.
Martin Hellman
Ralph C. Merkle (1952)

8. 8
1977 - Rivest, Shamir and Adleman
Ron Rivest (1947), Adi Shamir (1952), and Leonard Adleman (1945) at the
Massachusetts Institute of Technology, made several attempts over the
course of a year to create a one-way function that was hard to invert.
Rivest and Shamir, as computer scientists, proposed many potential
functions, while Adleman, as a mathematician, was responsible for finding
their weaknesses. For a time, they thought what they wanted to achieve
was impossible due to contradictory requirements. In April 1977, they
spent Passover at the house of a student and drank a good deal of
Manischewitz wine before returning to their homes at around midnight.
Rivest, unable to sleep, lay on the couch with a math textbook and started
thinking about their one-way function. He spent the rest of the night
formalizing his idea, and he had much of the paper ready by daybreak.
source: https://en.wikipedia.org/

9. Asymmetric Cryptography
With a key pair of which one is
private and the other is public, it
becomes possible to exchange
information in a secure way in the
absence of a secure channel
The public key is used to encrypt
and the private key to decrypt
9

10. Digital Signature
But we can use the keys also in the opposite
sequence, ie we can use the private key to
decipher (!) a data that is "clear text" - as if it were
an enciphered data.
The result is an unreadable "deciphered" data that
only if "enciphered" with the corresponding public
key regenerates the starting clear text message
Since only the owner of the private key can
generate it (deciphering), that strange
"deciphered" data is a signature!
10

11. Encryption and Signature
11
Hello Alice!
010010010
110111001
011000000
0
101010011
010010100
0110100111
encryption message signature
decipher
encipher verify
sign

12. 12
Standards

13. 13
The critical connection between identity and key
How to guarantee the signer identity?
● Certification Authority (CA)
How to ensure that the signer has exclusive control of the private key?
● Hardware Security Module (HSM) and SmartCard
● Two Factor Authentication (2FA)
How to manage the end of the exclusive control of the key before the
expiration date?
● Revocation process
● Certificate Revocation List (CRL)
● Online Certificate Status Protocol (OCSP)
● Timestamp Service Authority (TSA)
User Private Key

14. 14
Secure Signature Creation Device

15. 15
Smart Card

16. 16
RSA (1977) - Public Key Cryptography Standards
Id Name Comments
PKCS#7 Cryptographic
Message Syntax
Standard
See RFC 2315. Used to sign and/or encrypt messages under a PKI. Used also for
certificate dissemination (for instance as a response to a PKCS #10 message). Formed
the basis for S/MIME, which is as of 2010 based on RFC 5652, an updated Cryptographic
Message Syntax Standard (CMS). Often used for single sign-on.
PKCS#10 Certification
Request Standard
See RFC 2986. Format of messages sent to a certification authority to request
certification of a public key. See certificate signing request.
PKCS#11 Cryptographic
Token Interface
Also known as "Cryptoki". An API defining a generic interface to cryptographic tokens
(see also hardware security module). Often used in single sign-on, public-key
cryptography and disk encryption[10] systems. RSA Security has turned over further
development of the PKCS #11 standard to the OASIS PKCS 11 Technical Committee.
PKCS#12 Personal
Information
Exchange Syntax
Standard
See RFC 7292. Defines a file format commonly used to store private keys with
accompanying public key certificates, protected with a password-based symmetric key.
PFX is a predecessor to PKCS #12.
This container format can contain multiple embedded objects, such as multiple
certificates. Usually protected/encrypted with a password. Usable as a format for the Java
key store and to establish client authentication certificates in Mozilla Firefox. Usable by
Apache Tomcat.
source: https://en.wikipedia.org/

17. 17
RFC5280 - PKIX: Public Key Infrastructure (X.509)
Following is a simplified view of the architectural model assumed by the Public-Key Infrastructure using
X.509 (PKIX) specifications. The components in this model are:
● end entity: user of PKI certificates and/or end user system that is the subject of a certificate;
● CA: certification authority;
● RA: registration authority, i.e., an optional system to which a CA delegates certain
management functions;
● CRL issuer: a system that generates and signs CRLs; and
● repository: a system or collection of distributed systems that stores certificates and CRLs and
serves as a means of distributing these certificates and CRLs to end entities.

18. 18
RFC5280 - PKIX: Public Key Infrastructure (X.509)

19. 19
RFC5652 - Cryptographic Message Syntax
This document describes the Cryptographic Message Syntax (CMS). This syntax is
used to digitally sign, digest, authenticate, or encrypt arbitrary message content.
The CMS describes an encapsulation syntax for data protection. It supports
digital signatures and encryption. The syntax allows multiple encapsulations; one
encapsulation envelope can be nested inside another. Likewise, one party can
digitally sign some previously encapsulated data. It also allows arbitrary
attributes, such as signing time, to be signed along with the message content, and
it provides for other attributes such as countersignatures to be associated with a
signature.
The CMS can support a variety of architectures for certificate-based key
management, such as the one defined by the PKIX (Public Key Infrastructure
using X.509) working group [PROFILE].

20. 20
RFC5652 - Cryptographic Message Syntax (simplified)

21. 21
RFC3161 Time-Stamp Protocol (TSP)

22. eIDAS: l’identità digitale a valore legale
electronic IDentification Authentication and Signature
eIDAS is the basis for the construction of the Digital Single
Market in Europe
eIDAS requires interoperability throughout Europe from
1/7/2016
The Qualified Electronic Signature has legal value equivalent to
the handwritten one
The Regulation implies mandatory adoption for all Member
States
22

23. 23
European Telecommunications Standards Institute
ETSI plays a key role in supporting regulation and legislation with technical standards
and specifications. To do this they cooperate with other organizations including:
● the European Commission (EC)
● the European Free Trade Association (EFTA)
● the Electronic Communications Committee (ECC) of the European Conference of
Postal and Telecommunications Administrations (CEPT)
● Supporting European regulation & legislation
ETSI produces standards to support European regulation and legislation. These are
defined in Regulations, Directives and Decisions developed by the EU.

24. 24
ETSI Advanced Electronic Signatures
For an electronic signature to be considered as advanced, it must meet several
requirements:
● The signatory can be uniquely identified and linked to the signature
● The signatory must have sole control of the signature creation data (typically
a private key) that was used to create the electronic signature
● The signature must be capable of identifying if its accompanying data has
been tampered with after the message was signed
● In the event that the accompanying data has been changed, the signature
must be invalidated

25. 25
ETSI Advanced Electronic Signatures
Advanced electronic signatures that are compliant with eIDAS may be technically
implemented through the Ades Baseline Profiles that have been developed by the European
Telecommunications Standards Institute (ETSI):
● CAdES, CMS Advanced Electronic Signatures is a set of extensions to Cryptographic
Message Syntax (CMS) signed data making it suitable for advanced electronic
signatures.
● PAdES, PDF Advanced Electronic Signatures is a set of restrictions and extensions to PDF
and ISO 32000-1 making it suitable for Advanced Electronic Signature.
● XAdES, XML Advanced Electronic Signatures is a set of extensions to XML-DSig
recommendation making it suitable for Advanced Electronic Signatures.
● ASiC Baseline Profile. ASiC (Associated Signature Containers) specifies the use of
container structures to bind together one or more signed objects with either advanced
electronic signatures or time-stamp tokens into one single digital (zip) container.

26. 26
ISO 32000-1:2008 - Portable Document Format
ISO 32000-1:2008 specifies a digital form for representing
electronic documents to enable users to exchange and
view electronic documents independent of the
environment in which they were created or the
environment in which they are viewed or printed. It is
intended for the developer of software that creates PDF
files (conforming writers), software that reads existing PDF
files and interprets their contents for display and
interaction (conforming readers) and PDF products that
read and/or write PDF files for a variety of other purposes
(conforming products).

27. 27
PAdES - PDF Advanced Electronic Signatures
ETSI - TS 102 778-1 - Electronic Signatures and Infrastructures (ESI)

28. 28
Electronic Signatures and Infrastructures
source: ETSI TS 119 102-1

29. 29
Qualified Electronic Signature Creation Device
QSCD is a Secure Signature Generation Device that is certified and approved for
being used to generate Qualified Electronic Signatures (QES).
It uses technical and procedural means to ensure:
• Signing keys are kept secret
• Signing keys are created using established cryptographic techniques
• Signing keys can only be used by the right owner
• Compliance to the stringent standards for QES.

30. 30
Qualified Trust Service Provider

31. 31
eIDAS Qualified Electronic Signature
A qualified electronic signature is:
● an advanced electronic signature
● with a qualified digital certificate
● that has been created by a qualified trust service provider (QTSP)
● using a qualified signature creation device (QSCD)

32. 32
Digital Identity

33. 33
Digital Identity in EU - Today

34. 34
Digital Identity in Italy - Today
● Qualified Electronic Signature: users > 20 Mln, signs > 3 Bln/yr (AGID 2020)
● SPID (Sistema Pubblico Identità Digitale): 34 % of population (Oss. Poli Mi 2021)
● PEC (Posta Elettronica Certificata): users > 11 Mln, msgs > 3 Bln/yr (AGID 2020)
● eIDAS - Chapter II - Electronic Identification - (?)
● CID (Carta d'Identità Digitale) - No PIN no party!

35. 35
Digital Identity in EU - Tomorrow
The Commission will soon propose a secure European e-identity. One that we
trust and that any citizen can use anywhere in Europe to do anything from paying
your taxes to renting a bicycle. A technology where we can control ourselves what
data and how data is used.
Ursula von der Leyen
President of the European Commission
16 September 2020

36. 36
Digital Identity in EU - Challenges
● Levels of Assurance: Onboarding, AML/KYC, Legal Transactions, ...
● Model: Federated Trusted Identity Providers (or Self Sovereign Identity?)
● Technology: OAuth/SAML/OpenID-Connect (or SSI/EBSI/…?)
● Economic incentives to interoperability and standards adoption
● Monetization of the identification process carried by Identity Providers
● Governance Framework

37. 37
Decentralization

38. 38
1991 - Pretty Good Privacy
Zimmermann had been a long-time anti-nuclear activist, and created PGP
encryption so that similarly inclined people might securely use BBSs and securely
store messages and files. No license fee was required for its non-commercial use,
and the complete source code was included with all copies.
PGP found its way onto the Internet and rapidly acquired a considerable following
around the world. Users and supporters included dissidents in totalitarian
countries (some affecting letters to Zimmermann have been published, some of
which have been included in testimony before the US Congress), civil libertarians
in other parts of the world (see Zimmermann's published testimony in various
hearings), and the 'free communications' activists who called themselves
cypherpunks (who provided both publicity and distribution); decades later,
CryptoParty activists did much the same via Twitter.
source: https://en.wikipedia.org/

39. 39
1992 - The Web of Trust
The web of trust concept was first put forth by PGP creator Phil Zimmermann in
1992 in the manual for PGP version 2.0:
As time goes on, you will accumulate keys from other people that you may want
to designate as trusted introducers. Everyone else will each choose their own
trusted introducers. And everyone will gradually accumulate and distribute with
their key a collection of certifying signatures from other people, with the
expectation that anyone receiving it will trust at least one or two of the
signatures. This will cause the emergence of a decentralized fault-tolerant web
of confidence for all public keys.
source: https://en.wikipedia.org/

40. 40
1997 - OpenPGP
In July 1997, PGP Inc. proposed to the IETF that there be a standard called
OpenPGP. The IETF accepted the proposal and started the OpenPGP Working
Group. OpenPGP is on the Internet Standards Track and is under active
development. Many email clients provide OpenPGP-compliant email security as
described in RFC 3156. The current specification is RFC 4880 (November 2007),
the successor to RFC 2440. RFC 4880 specifies a suite of required algorithms
consisting of ElGamal encryption, DSA, Triple DES and SHA-1. In addition to these
algorithms, the standard recommends RSA as described in PKCS #1 v1.5 for
encryption and signing, as well as AES-128, CAST-128 and IDEA. Beyond these,
many other algorithms are supported. The standard was extended to support
Camellia cipher by RFC 5581 in 2009, and signing and key exchange based on
Elliptic Curve Cryptography (ECC) (i.e. ECDSA and ECDH) by RFC 6637 in 2012.
Support for ECC encryption was added by the proposed RFC 4880bis in 2014.
source: https://en.wikipedia.org/

41. 41
Resources
GNU Privecy Guard
https://gnupg.org/
Signing Your Code with Git
https://git-scm.com/book/en/v2/Git-Tools-Signing-Your-Work
Key Server
https://en.wikipedia.org/wiki/Key_server_(cryptographic)
On Digital Signatures and Key Verification
https://www.qubes-os.org/security/verifying-signatures/

42. 42
Hal Finney
Harold Thomas Finney II (May 4, 1956 –
August 28, 2014) was a developer for PGP
Corporation, and was the second
developer hired after Phil Zimmermann. In
his early career, he was credited as lead
developer on several console games.
He also was an early bitcoin contributor
and received the first bitcoin transaction
from bitcoin's creator Satoshi Nakamoto.
source: https://en.wikipedia.org/

43. 43
Timestamping Complementarity
PKI-TSA Bitcoin-OTS
A standard with legal value that has been around for a long time Not yet a standard
A service that depends on a central trustee A service based on a permissionless, resilient and decentralized
system, without a single point of failure
Verifying a timestamp requires the involvement of the original
issuing TSA
Anyone can verify the timestamp autonomously running a Bitcoin full
node or connecting to any trusted block explorer
Usually a TSA undertakes to guarantee the validity of a timestamp
for no more than twenty years
There is no predefined limit to the validity of an OTS timestamp, the
system aims to survive perpetually
The service of qualified TSAs usually has a specific cost per single
attestation
The service is free of charge for clients and the cost for the provider
is very low (a negligible fee for a small Bitcoin transaction,
approximately every hour, no matter how many requests are
aggregated each time)
The timestamp issue is immediate The time attestation in the form of a promise is immediate, its
upgrade takes about an hour
Timestamps can reach fractional second precision The time attestation proves data existence only in an interval of
hours
"Chaining up Time" https://ssrn.com/abstract=3743330

44. 44
Tools

45. 45
Distrust the infrastructure
Check the validity
● Check the integrity
● Check the authenticity
○ Check the ownership of the key
○ Check the expiration and revocation
○ Check the signature date and time

46. 46
Browser

47. 47
Acrobat

48. 48
OpenSSL
Get and read a CRL
● openssl crl2pkcs7 -in example.crl -out example.p7m
● openssl pkcs7 -in example.p7m -print
Get and read a Timestamp Response
● openssl ts -query -data file.png -no_nonce -sha512 -cert -out file.tsq
● curl -H "Content-Type: application/timestamp-query" --data-binary
'@file.tsq' https://freetsa.org/tsr > file.tsr
● openssl ts -reply -in file.tsr -text

49. 49
Resources
Verify
https://vol.ca.notariato.it/it
Italian Trusted LIST
https://www.agid.gov.it/it/piattaforme/firma-elettronica-qualificata/certificati
EU Trusted LIST (Root CA Certs)
https://webgate.ec.europa.eu/tl-browser/#/

50. 50
Grazie!
Emanuele CIsbani
ecisbani@intesigroup.com
30-03-2021 - Università Milano Bicocca