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73
README.md
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@ -8,24 +8,12 @@ Secrets hold sensitive information
The Secret interface manages limited time access to a secret and securely erases the secret when no longer needed.
Multiple `Secret` classes exist. Most of the time you shouldn't need to change the `Secret` type. The cryptographic library should have sane defaults.
Multiple `Secret` classes exist. Most of the time you shouldn't need to change the `Secret` type - the cryptographic library should have sane defaults.
If you have a high security or high performance application see [which secret type should I use?](https://didactic-drunk.github.io/crypto-secret.cr/main/Crypto/Secret.html)
## What attacks does a Secret protect against?
* Timing attacks when comparing secrets by overriding `==`
* Leaking data in to logs by overriding `inspect`
* Wiping memory when the secret is no longer in use
### Provided secret classes
* `Crypto::Secret::Guarded` - Guard pages, mprotect, doesn't appear in core dumps (os dependent)
* `Crypto::Secret::Bidet` - Wipe only. Low overhead.
* `Crypto::Secret::Not` - It's not secret. Doesn't wipe and no additional protection.
* `Crypto::Secret::Todo` - Uses mlock, mprotect and canaries in future versions
Secret providers may implement additional protections via:
* `#noaccess`, `#readonly` or `#readwrite` via `mprotect`
* `#noaccess`, `#readonly` or `#readwrite`
* Using [mprotect]() to control access
* Encrypting the data when not in use
* Deriving keys on demand from a HSM
* Preventing the Secret from entering swap ([mlock]())
@ -40,7 +28,7 @@ Secret providers may implement additional protections via:
```yaml
dependencies:
crypto-secret:
github: didactic-drunk/crypto-secret.cr
github: didactic-drunk/crypto-secret
```
2. Run `shards install`
@ -56,11 +44,12 @@ Secret providers may implement additional protections via:
```crystal
require "crypto-secret/bidet"
secret = Crypto::Secret.for(32, :secret_key)
# Bidet is a minimal but fast secret implementation
secret = Crypto::Secret::Bidet.new 32
# Don't forget to wipe!
secret.wipe do
secret.readonly do |slice|
# May only read from slice
# May only read slice
end
secret.readwrite do |slice|
# May read or write to slice
@ -89,28 +78,10 @@ secret = Crypto::Secret::Bidet.move_from slice # erases slice
# or
secret = Crypto::Secret::Bidet.copy_from slice
# or
secret = Crypto::Secret::Bidet.new size_in_bytes
secret = Crypto::Secret::Bidet size_in_bytes
secret.move_from slice
```
### Optionally change the security level
The default should be sufficient for most applications. Do not change unless you have special needs.
Password managers or cryptocurrency wallets may prefer :strong or :paranoid.
Blockchain verifiers or apps that only handle high volume public info may prefer :lax.
```crystal
# Choose one
Crypto::Secret::Config.setup :paranoid
Crypto::Secret::Config.setup :strong
#Crypto::Secret::Config.setup :default # automatic
Crypto::Secret::Config.setup :lax
```
See [#setup](https://didactic-drunk.github.io/crypto-secret.cr/main/Crypto/Secret/Config.html) for further information.
## What is a Secret?
<strike>Secrets are Keys</strike>
@ -122,8 +93,8 @@ That's complicated and specific to the application. Some examples:
Not secrets:
* `Digest` output. Except when used for key derivation, then it's a Secret, including the Digest state
* `IO::Memory` or writing a file. Except when the file is a password vault, cryptocurrency wallet, encrypted mail/messages, goat porn, maybe "normal" porn, sometimes scat porn, occassionally furry, not people porn
* Digest output. Except when used for key derivation, then it's a Secret, including the Digest state
* IO::Memory or writing a file. Except when the file is a password vault, cryptocurrency wallet, encrypted mail/messages, goat porn, maybe "normal" porn, sometimes scat porn, occassionally furry, not people porn
## Why?
@ -157,9 +128,9 @@ end
key = ...another Secret...
encrypted_str = File.read("filename")
decrypted_size = encrypted_str.bytesize - mac_size
file_secret = Crypto::Secret.for(decrypted_size, :data)
file_secret = Crypto::Secret::Large.new decrypted_size
file_secret.wipe do
file_secret.readwrite do |slice|
file_secrets.readwrite do |slice|
decrypt(key: key, src: encrypted_str, dst: slice)
# Do something with file contents in slice
@ -188,13 +159,26 @@ Example:
class SimplifiedEncryption
# Allow users of your library to provide their own Secret key. Also provide a sane default.
def encrypt(data : Bytes | String, key : Secret? = nil) : {Secret, Bytes}
key ||= Crypto::Secret.for(key_size, :secret_key)
key ||= Crypto::Secret::Default.random
...
{key, encrypted_slice}
end
end
```
## What attacks does a Secret protect against?
* Timing attacks when comparing secrets by overriding `==`
* Leaking data in to logs by overriding `inspect`
* Wiping memory when the secret is no longer in use
Each implementation may add additional protections
* `Crypto::Secret::Key` - May use mlock, mprotect and canaries in future versions
* `Crypto::Secret::Large` - May use mprotect in future versions
* `Crypto::Secret::Not` - It's not secret. Doesn't wipe and no additional protection.
## Other languages/libraries
* rust: [secrets](https://github.com/stouset/secrets/)
@ -207,7 +191,7 @@ end
**Only intended for use by crypto library authors**
```crystal
```
class MySecret < Crypto::Secret
# Choose one
include Crypto::Secret::Stateless
@ -229,8 +213,7 @@ class MySecret < Crypto::Secret
# return the size
end
# if Stateful provide [noaccess_impl, readonly_impl, readwrite_impl]
# optionally override [noaccess, readonly, readwrite]
# optionally override (almost) any other method with an implementation specific version
end

5
shard.yml
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@ -6,9 +6,4 @@ authors:
crystal: ">= 0.37"
dependencies:
mmap:
github: crystal-posix/mmap.cr
version: ">= 0.4.0"
license: MIT

21
spec/crypto_secret_spec.cr
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@ -4,29 +4,12 @@ require "../src/crypto-secret"
test_secret_class Crypto::Secret::Not
test_secret_class Crypto::Secret::Bidet
test_secret_class Crypto::Secret::Guarded
describe Crypto::Secret do
it ".for" do
[:kgk, :secret_key, :public_key, :data, :not].each do |sym|
secret = Crypto::Secret.for 2, sym
[:kgk, :key, :data, :not].each do |sym|
secret = Crypto::Secret.for sym, 2
secret.bytesize.should eq 2
end
end
it ".for fallback" do
secret = Crypto::Secret.for 2, :a, :b, :not
secret.bytesize.should eq 2
end
it ".for missing" do
expect_raises(KeyError) do
Crypto::Secret.for 2, :a
end
end
it ".random" do
secret = Crypto::Secret.random 2, :a, :b, :not
secret.bytesize.should eq 2
end
end

25
src/crypto-secret/config.cr
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@ -1,11 +1,10 @@
require "./not"
require "./bidet"
require "./guarded"
{% if @type.has_constant?("Sodium") %}
CRYPTO_SECRET_KEY_CLASS = Sodium::SecureBuffer
{% else %}
CRYPTO_SECRET_KEY_CLASS = Crypto::Secret::Guarded
CRYPTO_SECRET_KEY_CLASS = Crypto::Secret::Bidet
{% end %}
module Crypto::Secret::Config
@ -13,34 +12,26 @@ module Crypto::Secret::Config
USES = Hash(Symbol, Secret.class).new
enum SecurityLevel
# mlocks everything (including data)
Paranoid
# wipes everything
Strong
# balance between performance and wiping
Default
# performance
Lax
# None
end
def self.setup(level : SecurityLevel = :default) : Nil
register_use Not, :not, :public_key
def self.setup(level : SecurityLevel = SecurityLevel::Default) : Nil
register_use Not, :not
case level
in SecurityLevel::Paranoid
register_use Bidet, :not
register_use Guarded, :public_key
register_use CRYPTO_SECRET_KEY_CLASS, :kgk, :secret_key, :data
in SecurityLevel::Strong
register_use Bidet, :not, :public_key
register_use Crypto::Secret::Guarded, :data
register_use CRYPTO_SECRET_KEY_CLASS, :kgk, :secret_key
register_use CRYPTO_SECRET_KEY_CLASS, :kgk, :key, :data
in SecurityLevel::Default
register_use Crypto::Secret::Bidet, :data
register_use CRYPTO_SECRET_KEY_CLASS, :kgk, :secret_key
register_use CRYPTO_SECRET_KEY_CLASS, :kgk, :key
in SecurityLevel::Lax
register_use Bidet, :kgk, :secret_key, :data
register_use Bidet, :kgk, :key, :data
# in SecurityLevel::None
# register_use Not, :kgk, :key, :data
end
end

13
src/crypto-secret/crystal.cr
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@ -1,13 +0,0 @@
abstract class Digest
def update(data : Crypto::Secret)
data.readonly do |slice|
update slice
end
end
def final(data : Crypto::Secret)
data.readwrite do |slice|
final slice
end
end
end

47
src/crypto-secret/guarded.cr
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@ -1,47 +0,0 @@
require "./stateful"
require "mmap"
abstract class Crypto::Secret
# * Wipes on finalize but should not be relied on
# * Not locked in memory
# * Access protected
# * Guard pages
# * Won't appear in core dumps (some platforms)
class Guarded < Secret
include Stateful
protected getter buffer_bytesize : Int32
@dregion : Mmap::SubRegion
@data : Mmap::SubRegion
def initialize(size : Int32)
ps = Mmap::PAGE_SIZE
pages = (size.to_f / ps).ceil + 2
msize = pages * ps
@buffer_bytesize = size
@mmap = Mmap::Region.new(msize)
@mmap[0, ps].guard_page
@mmap[(pages - 1) * ps, ps].guard_page
@dregion = @mmap[ps, (pages - 2) * ps]
@dregion.crypto_key
@data = @dregion[0, size]
end
protected def readwrite_impl : Nil
@dregion.readwrite
end
protected def readonly_impl : Nil
@dregion.readonly
end
protected def noaccess_impl : Nil
@dregion.noaccess
end
delegate_to_slice @data
end
end

36
src/crypto-secret/secret.cr
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@ -1,13 +1,11 @@
require "./lib"
require "./class_methods"
require "./crystal"
# Interface to hold sensitive information (often cryptographic keys)
#
# ## Which class should I use?
# * `Crypto::Secret::Todo` - Use with small (<= 4096 bytes) keys
# * `Crypto::Secret::Guarded` - Use for decrypted data that may stress mlock limits
# * `Crypto::Secret::Bidet` - Wipe only with no other protection. General use and fast.
# * `Crypto::Secret::Key` - Use with small (<= 4096 bytes) keys
# * `Crypto::Secret::Large` - Use for decrypted data that may stress mlock limits
# * `Crypto::Secret::Not` - Only use when you're sure the data isn't secret. 0 overhead. No wiping.
#
# Other shards may provide additional `Secret` types ([sodium.cr](https://github.com/didactic-drunk/sodium.cr))
@ -33,36 +31,22 @@ abstract class Crypto::Secret
Readwrite
end
macro inherited
extend ClassMethods
end
def self.new(size : Int32)
raise NotImplementedError.new("workaround for lack of `abstract def self.new`")
end
# def self.random(size : Int32, *uses : Symbol, *, random = Random::Secure) : Crypto::Secret
def self.random(size : Int32, *uses : Symbol, **options) : Crypto::Secret
rand = options[:random]? || Random::Secure
for(size, *uses).random(random: rand)
end
def self.for(size : Int32, *uses : Symbol) : Crypto::Secret
for(*uses).new(size)
end
def self.for(size : Int32, secret : Crypto::Secret) : Crypto::Secret
raise ArgumentError.new("") unless size == secret.bytesize
def self.for(secret : Crypto::Secret) : Crypto::Secret
secret
end
def self.for(*uses : Symbol) : Crypto::Secret.class
uses.each do |use|
if klass = Config::USES[use]?
return klass
def self.for(use : Symbol, size : Int32) : Crypto::Secret
for(use).new(size)
end
end
raise KeyError.new("missing #{uses}, have #{Config::USES.keys}")
def self.for(use : Symbol) : Crypto::Secret.class
Config::USES[use]
end
# For debugging. Leaks the secret
@ -101,9 +85,9 @@ abstract class Crypto::Secret
end
# Fills `Secret` with secure random data
def random(random = Random::Secure) : self
def random : self
readwrite do |slice|
random.random_bytes slice
Random::Secure.random_bytes slice
end
self
end

18
src/crypto-secret/stateful.cr
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@ -1,13 +1,13 @@
require "./secret"
# Development guide:
# 1. Create your initialize method and optionally allocate memory
# 2. Create a finalize method to deallocate memory if necessary
# 3. Fill in the missing abstract methods
# 4. Optionally override any included methods (especially wipe_impl if the secret is not held in the provided slice)
# 5. Provide and test a dup method or raise on dup if not possible
#
# When state changes are required (such as using #noaccess) and the buffer is accessed from multiple threads wrap each #readonly/#readwrite block in a lock.
# Development guide:
# 1. Create your initialize method and optionally allocate memory
# 2. Create a finalize method to deallocate memory if necessary
# 3. Fill in the missing abstract methods
# 4. Optionally override any included methods (especially wipe_impl if the secret is not held in the provided slice)
# 5. Provide and test a dup method or raise on dup if not possible
#
# When state changes are required (such as using #noaccess) and the buffer is accessed from multiple threads wrap each #readonly/#readwrite block in a lock.
module Crypto::Secret::Stateful
@state = State::Readwrite
@pre_wipe_state = State::Readwrite
@ -119,4 +119,4 @@ module Crypto::Secret::Stateful
protected abstract def readwrite_impl : Nil
protected abstract def readonly_impl : Nil
protected abstract def noaccess_impl : Nil
end
end