DAVID ACLAND - DIGITAL SIGNATURES Introducon > whoami WHOAMI

David Acland @davidacland Introducon > whoami Introducon > About this talk

ABOUT THIS TALK Introducon > About this talk > Progress

Progress Bar Where are we? Introducon > About this talk > What WHAT WE’RE TALKING ABOUT Cryptology

Cryptography Cryptanalysis

Asymmetric Symmetric

Encrypon Digital Signatures Introducon > About this talk > Why WHY WE’RE TALKING ABOUT IT DNSSEC Signed Packages Gatekeeper TCC Secure boot

SSL DKIM AutoPkg

SSH Kernel Extensions Introducon > About this talk > Why WHY WE’RE TALKING ABOUT IT Introducon > About this talk > Why WHY WE’RE TALKING ABOUT IT Trusted signatures are becoming a requirement Introducon > About this talk > Contents CONTENTS

▸ Introducon to digital signatures ▸ Underlying technologies ▸ Praccal usage Introducon > About this talk > Warning

THERE’S MATHS IN HERE (sorry) Introducon > About this talk > Follow along

IT’S INTERACTIVE

https://bit.ly/2TR6y9a Introducon > Introducon to digital signatures

INTRODUCTION TO DIGITAL SIGNATURES Introducon > Introducon to digital signatures

WHAT IS A SIGNATURE? Introducon > Introducon to digital signatures > What’s a signature? WHAT’S A SIGNATURE? Introducon > Introducon to digital signatures > What’s a signature? WHAT DO THEY GIVE YOU?

▸ Authencaon ▸ Integrity Security Services ▸ Non-repudiaon Introducon > Introducon to digital signatures > Paper Signatures

ARE PAPER SIGNATURES EFFECTIVE? Introducon > Introducon to digital signatures > Paper Signatures ARE PAPER SIGNATURES EFFECTIVE?

▸ Authencity - You can’t be sure the sender is who they claim to be ▸ Integrity - You can change the contents aer it’s been signed ▸ Non-repudiaon - I can just deny I signed it Introducon > Introducon to digital signatures > Digital Signatures

WHAT ABOUT DIGITAL SIGNATURES? Introducon > Introducon to digital signatures > Digital Signatures DIGITAL SIGNATURES

▸ A private key is used to sign data ▸ It can be used to sign any data ▸ It provides the same security services as paper signatures Introducon > Introducon to digital signatures > What signing isn’t SIGNING ISN’T ENCRYPTION

▸ We send the plaintext data along with the signature ▸ Signatures aren’t interested in hiding the data UNDERLYING TECHNOLOGIES Underlying Technologies > Contents CONTENTS

▸ Hashing ▸ Asymmetric Cryptography ▸ Signing ▸ Cerficates and trust Underlying Technologies > Signing Process

BASIC SIGNING PROCESS Private Key

89630aafea14b2d8 ec9f0ca0251485cb Encryption Algorithm Hash function 94add8ec553218 1599b80051a09347 Data Hashed data

Public Key Hashed data 1d008bea0a8272da 89630aafea14b2d8 83842aa4d2f3f73e ec9f0ca0251485cb 9acd9c4dd76df908 Decryption Algorithm 94add8ec553218 435a567b55c6534e 1599b80051a09347 Signature Compare 89630aafea14b2d8 ec9f0ca0251485cb Hash function 94add8ec553218 1599b80051a09347 Underlying Technologies > Hashing

HASHING Underlying Technologies > Hashing WHAT IS HASHING?

Turns a data input into a fixed length, scrambled output

89630aafea14b2d8 ec9f0ca0251485cb9 Hash function 4add8ec5532181 599b80051a09347 Data Hex output Underlying Technologies > Hashing

A LITTLE HASHING DEMO Underlying Technologies > Hashing > Why use hashing

WHY USE HASHING? Private Key

Encryption Algorithm

Data

Public Key

1d008bea0a8272da 83842aa4d2f3f73e Decryption Algorithm 9acd9c4dd76df908 435a567b55c6534e Signature Compare Underlying Technologies > Hashing > Why use hashing WHY USE HASHING?

Original 1GB file:

Signed without hashing

Signed with hashing Underlying Technologies > Hashing > Algorithms

WHAT HASHING ALGORITHMS ARE AVAILABLE? Underlying Technologies > Hashing > Algorithms COMMON HASHING ALGORITHMS

▸ MD5 ▸ SHA-1 ▸ SHA-2 ▸ SHA-3 ▸ RIPEMD-160 ▸ Whirlpool ▸ BLAKE2 ▸ … Underlying Technologies > Hashing > Algorithms

WHAT HASHING ALGORITHMS ARE WEBSITES USING? Underlying Technologies > Hashing > Algorithms HASHING Underlying Technologies > Hashing > Algorithms HASHING Underlying Technologies > Hashing > Algorithms HASHING Underlying Technologies > Hashing > SHA256

A QUICK LOOK AT SHA256 Underlying Technologies > Hashing > SHA256 SHA256 Inial hash value 0101010101 Data 10011010000000001001101 AND 0001001101 = 0001001000 Underlying Technologies > Hashing > SHA256 SHA256 1. 1001101000 2. 0001001101 3. 0001001000 4. 0110100010 5. 1000000100 6. … 7. … 64. 1001011011 Underlying Technologies > Hashing > SHA256 AVALANCHE EFFECT

Single character change

hello Hello

Hash function Hash function

3362cec4339baf 89630aafea14b

Completely different output Underlying Technologies > Hashing > SHA256 SHA256 - LAST FEW STEPS Inial hash value 0001001000 AND + XOR Data 0101010101 89630aafea14b2d8ec9f0c Hash result a0251485cb94add8ec5 532181599b80051a09347 Underlying Technologies > Asymmetric Cryptography

ASYMMETRIC CRYPTOGRAPHY Underlying Technologies > Asymmetric Cryptography ASYMMETRIC CRYPTOGRAPHY

Symmetric (AES, 3DES, etc…) ABCD1234 ABCD1234

Private Public Asymmetric (RSA, DSA, etc…)

ABCD1234 EFGH5678 Underlying Technologies > Asymmetric Cryptography > SSL Handshake SSL HANDSHAKE

Private

Public Public

Symmetric Key Symmetric Key

Encrypt Decrypt Underlying Technologies > Asymmetric Cryptography > Signing SIGNING

Public

Verify Sign Public Private

Decrypt Encrypt Underlying Technologies > Signing

SIGNING Underlying Technologies > Signing SIGNING

The sender encrypts a hash of the data using their private key and a signature algorithm Underlying Technologies > Signing SIGNING

A LITTLE SIGNING DEMO Underlying Technologies > Signing > Signing Algorithms SIGNING

WHAT SIGNATURE ALGORITHMS ARE AVAILABLE? Underlying Technologies > Signing > Signing Algorithms SIGNING ▸ RSA ▸ Schnorr Signature Algorithm ▸ DSA ▸ Rapid Digital Signature ▸ ElGamal Encrypon System ▸ GMR Algorithm ▸ DSA ▸ Rabin Cryptosystem ▸ ECDSA ▸ EdDSA Algorithm ▸ GOST R 34 10-2012 ▸ Ed25519 Underlying Technologies > Signing > Signing Algorithms SIGNING

WHAT SIGNATURE ALGORITHMS ARE PEOPLE USING? Underlying Technologies > Signing > Signing Algorithms SIGNING Underlying Technologies > Signing > Signing Algorithms SIGNING Underlying Technologies > Signing > Signing Algorithms SIGNING Underlying Technologies > Signing > RSA

LET’S LOOK AT RSA Underlying Technologies > Signing > RSA RSA

▸ Asymmetric cryptographic algorithm ▸ Clifford Cocks in 1973 ▸ Ron Rivest, Adi Shamir, and Leonard Adleman in 1978 Underlying Technologies > Signing > RSA RSA - STEPS

▸ Key generaon ▸ Signing ▸ Verifying Underlying Technologies > Signing > RSA > Maths

SOME MATHS Underlying Technologies > Signing > RSA > Maths > Prime Numbers PRIME NUMBERS

A whole number (integer) greater than 1 that can not be made by mulplying other whole numbers

2 3 5 7 11 13 17 19 23… Underlying Technologies > Signing > RSA > Maths > Coprime COPRIME / RELATIVELY PRIME

Two integers are relavely prime if the only posive integer that divides them evenly is 1

e.g. 35 and 18 are relavely prime Underlying Technologies > Signing > RSA > Maths > Exponenaon EXPONENTIATION

Mulplying a number by itself n mes, where n is the exponent Base 24 Exponent

e.g. 24 = 2 x 2 x 2 x 2 = 16 Underlying Technologies > Signing > RSA > Maths > Factors FACTORS

Numbers that, when mulplied, produce another number 4 x 5 = 20 Factors Underlying Technologies > Signing > RSA > Maths > Factoring FACTORING

Given a number “n”, factoring is the process of working out the numbers, or “factors” that can be mulplied together to make “n”

e.g. for “20 = A x B”, find out what A and B are Underlying Technologies > Signing > RSA > Maths > Prime Factorisaon PRIME FACTORISATION

Given a number “n”, find two prime numbers that can be mulplied together to make “n”

e.g. for “15 = A x B”, find out what A and B are Underlying Technologies > Signing > RSA > Maths > PHI Φ (PHI) A count of the posive integers up to a given integer “n” that are relavely prime to “n” So if n = 6: Φ(6) = 2 1 2 3 4 5 6

1 and 5 share no factors with 6 Underlying Technologies > Signing > RSA > Maths > MOD MOD 32 mod 5 = 2 5 mod 8 = 5 38,927 mod 8 = 7 Underlying Technologies > Signing > RSA

RSA PROCESS Underlying Technologies > Signing > RSA > RSA Process RSA - KEY GENERATION

▸ Pick two prime numbers “p” & “q” ▸ Calculate the public key “n” by mulplying “p” and “q” ▸ Calculate Φ(n) ▸ Pick a public exponent “e”, that is coprime with Φ(n) ▸ Calculate the private key “d”, which is the inverse of e * (mod Φ(n)) Underlying Technologies > Signing > RSA > An Example

AN EXAMPLE… Underlying Technologies > Signing > RSA > An Example RSA - MULTIPLY P & Q p = 17 q = 19

17 * 19 = 323 n = 323 Underlying Technologies > Signing > RSA > An Example RSA - CALCULATE Φ(N) Φ(n) = Φ(p) * Φ(q) p = 17 q = 19 Φ(p) = p-1 Φ(q) = q-1 Φ(p) = 16 Φ(q) = 18 Φ(n) = 16 * 18 = 288 Underlying Technologies > Signing > RSA > An Example RSA - PICK A PUBLIC EXPONENT

11 must be coprime with Φ(n) Underlying Technologies > Signing > RSA > An Example RSA - CALCULATE THE INVERSE OF E * (MOD Φ(N)

11 288

131 Underlying Technologies > Signing > RSA > An Example RSA - FINAL VALUES

▸ n - Public323 (public key, the key) result of p * q ▸ e - Public11 (public exponent, exponent) needed to decrypt the signature ▸ d - Private131 (private key, the key) inverse of e * (mod Φ(n)) Underlying Technologies > Signing > RSA > An Example RSA - SIGNING

▸ Raise the message “m” to the power of the private key “d” ▸ Mod by the public key “n” md mod n Underlying Technologies > Signing > RSA > An Example RSA - SIGNATURE VERIFICATION

▸ Signature “s” raised to the power of the public exponent “e” ▸ Mod by the public key “n” se mod n Underlying Technologies > Signing > RSA > Where is the strength?

WHERE IS THE STRENGTH IN RSA? Underlying Technologies > Signing > RSA > Where is the strength? RSA

What are the factors of 15? 3 x 5 Underlying Technologies > Signing > RSA > Where is the strength? RSA

What are the factors of 133? 7 x 19 Underlying Technologies > Signing > RSA > Where is the strength? RSA

What are the factors of 526,301? 617 x 853 Underlying Technologies > Signing > RSA > Where is the strength?

RSA Example RSA “n” value:

25195908475657893494027183240048398571429282126204032027777137 83604366202070759555626401852588078440691829064124951508218929 85591491761845028084891200728449926873928072877767359714183472 70261896375014971824691165077613379859095700097330459748808428 40179742910064245869181719511874612151517265463228221686998754 91824224336372590851418654620435767984233871847744479207399342 36584823824281198163815010674810451660377306056201619676256133 84414360383390441495263443219011465754445417842402092461651572 33507787077498171257724679629263863563732899121548314381678998 85040445364023527381951378636564391212010397122822120720357 Underlying Technologies > Signing > Summary

SUMMARY OF THE SIGNING PROCESS Underlying Technologies > Signing > Summary SIGNING Step 1 Bob hashes the data using a hashing algorithm like SHA2 Underlying Technologies > Signing > Summary SIGNING Step 2 Bob encrypts the hash with his private key. The result is Bob’s digital signature Underlying Technologies > Signing > Summary SIGNING Step 3

The data is sent, along with the signature Underlying Technologies > Signing > Summary SIGNING Step 4 Alice decrypts the encrypted hash using Bob’s public key Underlying Technologies > Signing > Summary SIGNING Step 5 Alice hashes the plaintext data with the same hashing algorithm and compares the output with the hash provided in the digital signature Underlying Technologies > Cerficates

WHAT DO CERTIFICATES HAVE TO DO WITH SIGNING? Underlying Technologies > Cerficates CERTIFICATES

Name

Public Key Underlying Technologies > Cerficates > Trust

HOW CAN WE TRUST THE SENDER OF SIGNED DATA? Underlying Technologies > Cerficates > Self Signed Underlying Technologies > Cerficates > Self Signed Underlying Technologies > Cerficates > Trust TRUST

Trusted by macOS Presented by server Underlying Technologies > Cerficates > Trust TRUST Underlying Technologies > Cerficates > Trust INTEGRITY

www.apple1.com PRACTICAL USAGE Praccal Usage > Contents CONTENTS

▸ SSL website cerficates ▸ Signing a package ▸ Signing an app ▸ Autopkg & signatures ▸ KEXTs ▸ TCC ▸ Secure boot Praccal Usage > SSL website cerficates SSL WEBSITE CERTIFICATES

1. Create a private 2. Create Cerficate 3. 3rd party validates and key Request signs the request

4. Receive your signed cerficate Praccal Usage > Signing a package SIGNING A PACKAGE

▸ Get the signing cerficate ▸ Add to your keychain ▸ Sign packages Praccal Usage > Signing a package

GET THE DEV CERT AND SIGN A PACKAGE Praccal Usage > Signing an app SIGNING AN APP

▸ Get the signing cerficate ▸ Add to your keychain ▸ Sign apps Praccal Usage > Signing an app

SIGN AN APP Praccal Usage > Autopkg & signatures AUTOPKG & SIGNATURES You can do a code sign check…

Processor CodeSignatureVerifier Arguments input_path %pathname%/Office*.*pkg expected_authority_names Developer ID Installer: Microsoft Corporation (UBF8T346G9) Developer ID Certification Authority Apple Root CA Praccal Usage > Autopkg & signatures AUTOPKG & SIGNATURES And you can store a hash of the parent recipes…

ParentRecipeTrustInfo non_core_processors parent_recipes com.github.moofit.app.download path /RecipeRepos/autopkg.moofit-recipes/app.download.recipe sha256_hash 2d5f88ad49d80ecb5a73ebca844a7335f22741a3276a496240a12bf430c151de Praccal Usage > KEXTs KEXTS

▸ KEXTs are codesigned with the vendors developer key ▸ Users can approve the loading of the KEXTs ▸ Admins can whitelist the vendor or the specific KEXT with a profile ▸ All ed back to the Apple root cerficates via a chain of trust Praccal Usage > TCC TCC

▸ Similar to KEXTs in regards to signatures ▸ Uses the Team and Bundle idenfiers to grant apps access ▸ Also ed back to Apple via a chain of trust Praccal Usage > Secure Boot SECURE BOOT

▸ Each step of the boot process is cryptographically signed by Apple: ▸ T2 chip executes code in the Boot ROM ▸ The Boot ROM verifies the iBoot bootloader ▸ iBoot verifies the kernel extension code on the T2 chip ▸ The kernel extension code on the T2 chip verifies the Intel UEFI firmware ▸ UEFI firmware verifies the signature for boot.efi ▸ Boot.efi verifies the signature of a new file called immutablekernel THANKS