php[world] 2016 - Tales From the Crypto: A Cryptography Primer

@adam_englander
Tales From the Crypto
A Cryptography Primer

@adam_englander
We are going to talk about the common
methods and terms used for
cryptography in application development

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What is Cryptography?

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

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

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Good cryptography makes it
extremely difﬁcult to identify patterns
in the obscured data.

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Type of Cryptography We Will Cover
• Encryption/Decryption
• Digital Signatures
• Hashing

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Encrypting data ensures only
certain parties can read it.

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Encrypted data can be
decrypted.

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Encryption uses mathematical
algorithms called ciphers.

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The ciphers use secrets called
cipher keys.

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Cipher keys can be symmetric
(shared secrets) or asymmetric
(public key cryptography).

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Symmetric Key Encryption

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Symmetric key encryption applies
ciphers against data producing a
cipher text.

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There are two types of symmetric
key ciphers:
stream and block.

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Stream ciphers use a cipher key
with a cryptographically secure
pseudorandom cipher digit
stream called a keystream to
product the cipher text.

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Cryptographically secure
pseudorandom values are
issued to be random enough not
to generate distinguishable
patterns.

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Block ciphers execute against a
ﬁxed length group of bits.

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Cipher Block Execution Modes

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Electronic Cookbook (ECB)

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DO NOT USE ECB!

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Electronic cookbook encrypts
each block separately.

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It is not secure as patterns are
created from the same data resulting
in the same cipher text.

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If you manage to decrypt one block
of the cipher text, you can now
decrypt all of the others.

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Plain ECB CBC
Mode Comparison
Tux the Penguin, the Linux mascot. Created in 1996 by Larry Ewing with The GIMP.

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Block Chain and Feedback
Modes: CBC, CFB, and OFB

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All use an initialization vector (IV) to
provide the chain/feedback on the
ﬁrst block.

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All base the cipher value of the
current block on some portion of
the previous block.

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Unless you have a speciﬁc use
case, use CBC.

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Use PKCS7 padding as it is secure
and has the widest compatibility.

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Asymmetric Key Encryption:
Public Key Cryptography

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Public Key Cryptography use
key pairs, public/private.

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Public keys can be
disseminated to anyone.

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Public keys can encrypt data
but cannot decrypt the data it
encrypts.

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Private keys are secret.

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Public keys can encrypt and
decrypt data.

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Public Key Cryptography
Implementations

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RSA is the only form available in
PHP.

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RSA encryption is
computationally expensive
using very large prime integers
and exponential computation.

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RSA encryption is limited to the
amount of data it can encrypt
based on the size of the private
key.

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RSA encryption is often used to
exchange secret keys for
symmetric key encryption.

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The Difﬁe/Hellmen key exchange
in SSL/TLS is a great example.

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Difﬁe-Hellman Key
Exchange
The “Common Paint” is a random
number generated on the client and
encrypted with the public key from the
server. It is transmitted to the server and
decrypted using the private key. They
negotiate a shared secret and then
utilize symmetric key encryption with
that secret to communicate further.

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Always use PKCS1 OAEP Padding.
PKCS#1 v1.5 is the PHP default but
must not be used.

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Hashes can not be reversed. They
can only be recreated and veriﬁed.

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Hashing data is used to verify
the integrity of data or store the
data obscured.

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Electronic Signatures

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Hashes are used in conjunction with
secrets to create electronic
signatures.

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Symmetric Key Signatures

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Symmetric key signatures are known
as a Hash-based Message
Authentication Code or HMAC

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HMACs use a hashing algorithm in
combination with a shared secret to
generate a veriﬁable hash.

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The minimum hashing algorithm for
an HMAC is SHA-1. SHA-256 or
better is preferred.

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Key size determines the
cryptographic strength of the
signature.

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Asymmetric Key Signatures

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The private key is used to sign
the data.

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The public key is used to verify
the signature.

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RSA is the only asymmetric key
signature available in PHP.

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The amount of data RSA can sign is
based on the size of the private key.

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RSA uses hashing algorithms for
data larger than the key allows.

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SHA1 is the “suggested” minimum
hashing algorithm for RSA.

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Password Hashing

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Hashes are used for passwords
or any value that will be
presented for veriﬁcation.

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Proper password hashing is done
via a Key Derivation Function (KDF).

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Never use a standard hashing
algorithm for passwords EVER!

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Key derivation functions use a “salt”
to create differentiation for the same
password.

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Key derivation functions apply the
salted hash for a deﬁned iteration
count.

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Hashes must be cryptographically
pseudorandom and large.

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Iteration counts must be as
large as can be tolerated.

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HASH UNTIL IT HURTS!

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PHP provides PBKDF2 and
BCRYPT for password hashing.

@adam_englander
It also provides convenience functions:
http://php.net/manual/en/
ref.password.php

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Encrypt all data that is secret or
private.

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Sign all signiﬁcant data in
transit.

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Use the strongest encryption
you can support.

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Do NOT use rand() or mt_rand()
to generate keys or IVs. Use
Use random_bytes().
paragonie/random_compat is a
PHP 5.x polyﬁll.

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Use the OpenSSL extension for
everything but password hashing

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If you are writing a library, you
can use phpseclib/phpseclib as
an abstraction layer to
OpenSSL, MCrypt, or no crypto
extensions installed.

@adam_englander
Use
OPENSSL_PKCS1_OAEP_PADDING
for RSA encryption and
OPENSSL_ALGO_SHA256/384/512 for
signatures

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Use aes-256-cbc for symmetric
key encryption and
aes-256-cbc-hmac-sha256 for
symmetric key signatures

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Use built in password hashing
functions to do it right.

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Use a large number of iterations.
Shoot for at least 500ms of hashing.

@adam_englander
Further Reading
• http://php.net/manual/en/book.openssl.php
• http://php.net/manual/en/function.password-hash.php
• http://php.net/manual/en/book.csprng.php
• https://github.com/phpseclib/phpseclib
• Wikipedia

@adam_englander
Please Rate This Talk
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php[world] 2016 - Tales From the Crypto: A Cryptography Primer

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php[world] 2016 - Tales From the Crypto: A Cryptography Primer