The many benefits of a RESTful architecture has made it the standard way in which to design web based APIs. For example, the principles of REST state that we should leverage standard HTTP verbs in order to help keep our APIs simple. Server components that are considered RESTFul should be stateless which help to ensure that they can easily scale. However, the best practices of REST and security often seem to clash. How should sensitive information be transmitted in RESTful APIs? How should a user be authenticated in a stateless application? How is it possible to design an API so it is both secure and RESTful? Securing RESTful endpoints is further complicated by the the fact that security best practices evolve so rapidly. In this talk Rob will explore various ways to perform authentication in RESTful APIs. Along the way we will clear up misconceptions, explore common pitfalls, and discover new insights into authentication.

1. The State of Authenticating
RESTful APIs
@rob_winch

3. Authentication

4. Naïve approach…
4
https://api.example.com?username=r
ob&password=secret

5. Naïve approach…
5
https://api.example.com?username=r
ob&password=secret

6. “ Come on Bender. It's up to you
to make your own decisions in
life. That's what's separates
people and robots from
animals .. and animal robots!
Fry
Futurama

7. RFC-7231 Sensitive Information
7
“ Authors of services ought to avoid
GET-based forms for the submission
of sensitive data …
- RFC-7231: Section 9.4

8. Basic Authentication

9. Basic Authentication

10. Digest Authentication

11. Transport Layer Security (TLS)
• Confidentiality
• Integrity

13. Checking TLS
https://www.ssllabs.com/ssltes
t/
https://shaaaaaaaaaaaaa.com/

15. https://letsencrypt.org/
https://letsencrypt.org/

16. TLS Performance
• Computational overhead
• Latency overhead
• Cache

17. Adam Langley, Google
“On our production frontend machines, SSL/TLS
accounts for less than 1% of the CPU load, less than 10
KB of memory per connection and less than 2% of
network overhead.
https://goo.gl/IYJrqv

18. Doug Beaver, Facebook
“We have found that modern software-based TLS
implementations running on commodity CPUs are fast
enough to handle heavy HTTPS traffic load without
needing to resort to dedicated cryptographic hardware.
https://goo.gl/pf8Xwh

19. Jacob Hoffman-Andrews, Twitter
“HTTP keepalives and session resumption mean that
most requests do not require a full handshake, so
handshake operations do not dominate our CPU
usage.
https://goo.gl/Re0ijb

20. TLS Optimize
• TLS Resumption
• Latency
• Online Certificate Status Protocol (OCSP)
• Cloudflare
2
0

21. Optimizing TLS
Is TLS Fast Yet.com
21

22. HTTP Basic over HTTPS?
oclHashcat
Hash Type Speed
MD5 115.840 Bh/s
SHA1 37.336 Bh/s
SHA256 14.416 Bh/s
SHA512 4.976 Bh/s
Ubuntu 14.04, 64 bit
ForceWare 346.29
8x NVidia Titan X

23. Introduce Session
23
username=winch&name=Rob+Winch

24. Encrypting the Session
24
Base64(IV,
aes_cbc(k,IV,plainText))
• k – a secret key only known to server
• aes_cbc – encrypts the plainText using AES/CBC with the
provided IV
• plainText – format of username=winch&name=Rob+Winch

25. Your handwriting is atrocious,
not encrypted

26. Introduce Session
username=winch&name=Rob+Winch
username=admin&name=Rob+Winch
Can change properly encrypted value below:
To have the following Plaintext
https://goo.gl/2Uio0W

27. eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxM
jM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4
iOnRydWV9.TJVA95OrM7E2cBab30RMHrHDcEfxjoYZg
eFONFh7HgQ
JWT Encoded
Header
{
"alg": "HS256",
"typ": "JWT”
}
Payload
{
"sub": "1234567890",
"name": "John Doe",
"admin": true
}

28. HMACSHA256(
base64UrlEncode(header) + "." +
base64UrlEncode(payload),
“secret”
)
JWT Signature

29. 2:03 PM - 27 Jul 2015
https://goo.gl/Hs383Z

30. 10:54 AM - 28 May 2015
https://goo.gl/ZbP9Yp

31. eyJhbGciOiJub25lIiwidHlwIjoiSldUIn0.eyJzdWIiOiIxMjM
0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iO
nRydWV9.
JWT Encoded
Header
{
"alg": "none",
"typ": "JWT”
}
Payload
{
"sub": "1234567890",
"name": "John Doe",
"admin": true
}

32. eyJhbGciOiJub25lIiwidHlwIjoiSldUIn0.eyJzdWIiOiIxMjM
0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iO
nRydWV9. EkN-
DOsnsuRjRO6BxXemmJDm3HbxrbRzXglbN2S…
JWT Encoded
Header
{
"alg": "RS256",
"typ": "JWT”
}
Payload
{
"sub": "1234567890",
"name": "John Doe",
"admin": true
}

33. RSASHA256(
base64UrlEncode(header) + "." +
base64UrlEncode(payload),
Private RSA Key
)
Creating RSASHA256

34. RSASHA256(
base64UrlEncode(header) + "." +
base64UrlEncode(payload),
provided signature,
Public RSA Key
)
Verifying RSASHA256

35. Header
{
"alg": "HS256",
"typ": "JWT”
}
HMACSHA256(
base64UrlEncode(header) + "." +
base64UrlEncode(payload),
RSA Public Key
)
JWT Signature

37. “… each request from client to server must contain all
of the information necessary to understand the
request, and cannot take advantage of any stored
context on the server.
- Roy Fielding, Architectural Styles and
the Design of Network-based Software Architectures
http://goo.gl/MzVy0V
Roy Fielding

38. Representational STATE transfer
“… session state can be transferred by the
server to another service such as a database to
maintain a persistent state for a period and
allow authentication
- Wikipedia
http://goo.gl/bd33t7

40. Summary
• Do NOT place sensitive information in URL
• Use HTTPS everywhere
• Use “cached” credentials
• Security prefers State
@rob_winch
Presentation Available at
https://goo.gl/QTfCCW