Cryptography for Beginners - Sunshine PHP 2018

@adam_englander
Cryptography for Beginners
Adam Englander
Software Architect, iovation

@adam_englander
I am a Virtual Crime Fighter

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Let’s Set Some Expectations

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What is cryptography?

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–Wikipedia
“Cryptography…is the practice and
study of techniques for secure
communication in the presence of third
parties called adversaries.”

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How Cryptography Works

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How is cryptography used?

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Encryption Signatures
Key Derivation Hashing

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Asymmetric Encryption

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Symmetric Encryption

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Input MD5 SHA1
Foo
1356c67d7ad1638d816bfb82
2dd2c25d
201a6b3053cc1422d2c3670b6
2616221d2290929
Bar
ddc35f88fa71b6ef142ae61f35
364653
e496fd20136d4bb7828ebb0ab
925b1bd977208e4

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Collisions occur when two input
values create the same hash

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Any modern hashing algorithm will
never create collision for an input
value whose size is equal to or less
then the hash output size

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db110e4553b9fb646c8d01d928668046
33,571 byte input and 32 byte output

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Hashes by themselves aren’t very useful!

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Data Key Signature
Foo KeyOne b4ac60b7d319d41df60c99a6d064c18e
Foo KeyOne b4ac60b7d319d41df60c99a6d064c18e
Foo KeyTwo db97086208d9dd34d4b288959cac612f
Bar KeyOne 8624de374522eaf1b4ae9f0b872c2169

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Key Derivation

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ihatepasswords randomsalt gPqSXKzzeStBAqT3

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gPqSXKzzeStBAqT3 randomsalt hoEiNrLNefkxRNPR

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hoEiNrLNefkxRNPR randomsalt MgbfofelpvLjM0Hx

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MgbfofelpvLjM0Hx randomsalt xYjyM0wXf1VYboBa

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MgbfofelpvLjM0Hx randomsalt xYjyM0wXf1VYboBa
xYjyM0wXf1VYboBa randomsalt OpWKejkZt/u1wFCk

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How do I get good
cryptography?

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Good cryptography obscures data
in such a way that it is difﬁcult and
costly to duplicate or reverse.

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Attacking Cryptography

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There are ways to ﬁght all that
power...

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Algorithm Complexity

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System Resources

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–Oxford Dictionary
Entropy:
Lack of order or predictability; gradual
decline into disorder.”

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Real world data has very
predictable patterns.

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HTTP/1.1 200 OK
Content-Type: application/json
Server: Apache/2.1
Date: Thu, 08 Feb 2018 18:19:56 GMT
{
"account": "my-secret-account-number",
"date_of_birth": "1980-01-02",
"ﬁrst_name": "Jane",
"last_name": "Doe",
"ssn_last4": "1234",
}

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Credential data is highly
predictable

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Most services use email for the
username

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Passwords have very high
predictability and are reused

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–iovation: August 2015 Password Survey
https://s3.amazonaws.com/launchkey-blog/LaunchKey_Password_Survey_Results.pdf
“68% of people reuse passwords”

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–Keeper Security: The Most Common Passwords of 2016
https://keepersecurity.com/public/Most-Common-Passwords-of-2016-Keeper-Security-Study.pdf
“The top 25 passwords of 2016
constitute over 50% of the 10M
passwords that were analyzed.”

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–Keeper Security: The Most Common Passwords of 2016
https://keepersecurity.com/public/Most-Common-Passwords-of-2016-Keeper-Security-Study.pdf
“Nearly 17% of users are safeguarding
their accounts with “123456."”

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Most users will choose
passwords based on ease of
recall rather than entropy

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All the reuse and predictability
in passwords creates a very
serious problem

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user1 wI6Lx2klirB32K5T/4iQzsRVXI0PoVfc
user2 eHc9kCCZAzmR8HrelHeOAOs67XBo6OQe
user4 7U02IuFr4KJdjcexi26XFBWOuB3rTGLh

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Good cryptography uses random
salts to add entropy to hashes

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user1 4Ka7pm2M hqebP0ZRMl1DuBuoDC6+aA==
user2 lmsnAV/G XW0sV+kkle4DGaRyCul9mg==
user3 dLi1KjpE WrxmEs5ebHl1BiSp78fAeg==
user4 oRj3JUBE dATxMWkabTpBUwsjtNu3Eg==
user5 SD1sEqV tHKLSj5J8FoO0LHJfeI6lA==

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Nearly every type of data has
recognizable patterns

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English Message Patterns
• Spaces can be determined based on predictable word patterns
• Single letter words will be either the letter i or a
• In a two letter word, one of the letters is a vowel
• Three letter words mostly start and end with consonants and nearly
always have a vowel in the middle
• The letter e is the most common of all letters

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RrSRvtw/2Mk993TmCMjoAoSjyTAIF1emZQU=
RrSRvtw/2Mk993TmCMjoAoSjyTAIF1emZQU=
VXXo7Ov5OxFC5l6hEwDECoSjyTAIF1emZQY=
uoZjkwYzCwwN18xU8aZMzISjyTAIF1SmZQU=
yUe6wRXtblMRxrYP/N4n1ISjyTAIF1SmZQY=
coqei5pw+HHPDpaCPzcNW4SjyTMIF1emZQU=

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H4pyN6ucltNSlZBsaT5h2SBIuAXvITa0N3U=
uAHjDXC+A0QcyxLugng2wGd/QoghrgbHMaM=
o3O+HjdzJOZ7bZEi8X5MBbMWVphZmGnHEoQ=
RCsavNOf1KNgf7FAqn0o6xV/nWWMsT3KkNU=
dkHaoUx4npXSIOvO8rvY07CdWfOoQ7+Pht4=
rBdxOfwfsGmavqsgpqcavapMNb2/vYEFW6c=

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Random salts and IVs need
good random values

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Stop it! You’re blowing my mind!

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Use the password extension!

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<?php
function validate_password($password, $user) {
}

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<?php
if (!password_verify($password, $user->password)) {
throw new InvalidArgumentException("Password Failed");
}
}

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<?php
if (!password_verify($password, $user->password)) {
throw new InvalidArgumentException("Password Failed");
}
if (password_needs_rehash($user->password, PASSWORD_DEFAULT)) {
$user->password = password_hash($password, PASSWORD_DEFAULT);
$user->save();
}
}

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It’s encryption that’s good for you

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// Generating your encryption key
$key = random_bytes(SODIUM_CRYPTO_SECRETBOX_KEYBYTES);

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// Generate a random nonce
$nonce = random_bytes(SODIUM_CRYPTO_SECRETBOX_NONCEBYTES);

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// Using your key to encrypt information
$ciphertext = sodium_crypto_secretbox('test', $nonce, $key);

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// Using your key to encrypt information
$ciphertext = sodium_crypto_secretbox('test', $nonce, $key);
// Decrypting a message requires the nonce and key used to encrypt
$plaintext = sodium_crypto_secretbox_open($ciphertext, $nonce, $key);
if ($plaintext === false) {
throw new Exception("Bad ciphertext");
}

@adam_englander
Books
• The Code Book: The Science of Secrecy from
Ancient Egypt to Quantum Cryptography -
Simon Singh - ISBN: 0-385-49532
• Cryptography Engineering: Design Principles
and Practical Applications - Niels Ferguson,
Bruce Schneider, Tadayoshi Kohno - ISBN:
978-0-470-47424-2

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Websites
• https://secure.php.net/manual/en/book.password.php
• https://paragonie.com/book/pecl-libsodium
• https://secure.php.net/manual/en/book.openssl.php
• https://secure.php.net/manual/en/book.csprng.php
• https://en.wikipedia.org/wiki/Cryptography

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https://joind.in/talk/f411c

Cryptography for Beginners - Sunshine PHP 2018

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