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64 changes: 64 additions & 0 deletions
64
Sources/MessageAuthentication/MessageAuthenticationHash.swift
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,64 @@ | ||
| /// A hash that can be used to generate a message authentication code (MAC). | ||
| public | ||
| protocol MessageAuthenticationHash:RandomAccessCollection where Index == Int, Element == UInt8 | ||
| { | ||
| /// The natural block stride of this hash function. | ||
| static | ||
| var stride:Int { get } | ||
|
|
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| /// The output size, in bytes, of this hash function. | ||
| static | ||
| var count:Int { get } | ||
|
|
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| /// Computes an instance of this hash for the given message. | ||
| init<Message>(hashing message:Message) | ||
| where Message:Collection, Message.Element == UInt8 | ||
| } | ||
| extension MessageAuthenticationHash | ||
| { | ||
| @inlinable public | ||
| var endIndex:Int | ||
| { | ||
| self.startIndex + Self.count | ||
| } | ||
| @inlinable public | ||
| var count:Int | ||
| { | ||
| Self.count | ||
| } | ||
| } | ||
| extension MessageAuthenticationHash | ||
| { | ||
| /// Computes a hash-based message authentication code (HMAC) for | ||
| /// the given message using the given key. | ||
| /// | ||
| /// This initializer computes an instance of ``MessageAuthenticationKey`` | ||
| /// and uses it to generate an instance of ``Self``. If you are reusing | ||
| /// the same `key` multiple times, it is more efficient to compute the | ||
| /// message authentication key externally and call its | ||
| /// ``MessageAuthenticationKey.authenticate(_:)`` method instead. | ||
| @inlinable public | ||
| init<Message, Key>(authenticating message:Message, key:Key) | ||
| where Message:Sequence, Message.Element == UInt8, | ||
| Key:Collection, Key.Element == UInt8 | ||
| { | ||
| let key:MessageAuthenticationKey<Self> = .init(key) | ||
| self = key.authenticate(message) | ||
| } | ||
| } | ||
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| extension MessageAuthenticationHash | ||
| { | ||
| /// Derives an encryption key from a password and salt. | ||
| /// This is a password-based key derivation function | ||
| /// ([PBKDR2](https://en.wikipedia.org/wiki/PBKDF2)). | ||
| @inlinable public static | ||
| func pbkdf2<Password, Salt>(password:Password, salt:Salt, iterations:Int, | ||
| blocks:Int = 1) -> [UInt8] | ||
| where Password:Collection, Password.Element == UInt8, | ||
| Salt:Collection, Salt.Element == UInt8 | ||
| { | ||
| let key:MessageAuthenticationKey<Self> = .init(password) | ||
| return key.derive(salt: salt, iterations: iterations, blocks: blocks) | ||
| } | ||
| } |
80 changes: 80 additions & 0 deletions
80
Sources/MessageAuthentication/MessageAuthenticationKey.swift
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,80 @@ | ||
| /// A precomputed message authentication key, which can be used to compute | ||
| /// hash-based message authentication codes ([HMACs](https://en.wikipedia.org/wiki/HMAC)). | ||
| /// | ||
| /// Using this type to generate authentication codes for many messages with | ||
| /// the same base key is faster than repeatedly calling | ||
| /// ``MessageAuthenticationHash.init(authenticating:key:)``. | ||
| @frozen public | ||
| struct MessageAuthenticationKey<Hash> where Hash:MessageAuthenticationHash | ||
| { | ||
| public | ||
| let inner:[UInt8] | ||
| public | ||
| let outer:[UInt8] | ||
|
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| /// Creates a message authentication key from the given base key. | ||
| @inlinable public | ||
| init<Key>(_ key:Key) where Key:Collection, Key.Element == UInt8 | ||
| { | ||
| let normalized:[UInt8] | ||
| let count:Int = key.count | ||
| if count > Hash.stride | ||
| { | ||
| let key:Hash = .init(hashing: key) | ||
| normalized = [UInt8].init(key) + repeatElement(0, count: Hash.stride - Hash.count) | ||
| } | ||
| else if count < Hash.stride | ||
| { | ||
| normalized = [UInt8].init(key) + repeatElement(0, count: Hash.stride - count) | ||
| } | ||
| else | ||
| { | ||
| normalized = [UInt8].init(key) | ||
| } | ||
|
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| self.inner = normalized.map { $0 ^ 0x36 } | ||
| self.outer = normalized.map { $0 ^ 0x5c } | ||
| } | ||
| } | ||
| extension MessageAuthenticationKey | ||
| { | ||
| /// Computes a hash-based message authentication code | ||
| /// ([HMAC](https://en.wikipedia.org/wiki/HMAC)) for the given message | ||
| /// using this key. | ||
| @inlinable public | ||
| func authenticate<Message>(_ message:Message) -> Hash | ||
| where Message:Sequence, Message.Element == UInt8 | ||
| { | ||
| .init(hashing: outer + Hash.init(hashing: inner + message)) | ||
| } | ||
| /// Derives an encryption key using this message authentication key and | ||
| /// the given salt. If this message authentication key was computed from | ||
| /// a password, then this functions as a password-based key derivation | ||
| /// function ([PBKDR2](https://en.wikipedia.org/wiki/PBKDF2)). | ||
| @inlinable public | ||
| func derive<Salt>(salt:Salt, iterations:Int, blocks:Int = 1) -> [UInt8] | ||
| where Salt:Collection, Salt.Element == UInt8 | ||
| { | ||
| var output:[UInt8] = [] | ||
| output.reserveCapacity(blocks * Hash.count) | ||
| for block:UInt32 in 1 ... UInt32.init(blocks) | ||
| { | ||
| let salt:[UInt8] = withUnsafeBytes(of: block.bigEndian) { [UInt8].init(salt) + $0 } | ||
|
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| var hash:Hash = self.authenticate(salt) | ||
| var block:[UInt8] = .init(hash) | ||
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| for _ in 1 ..< iterations | ||
| { | ||
| hash = self.authenticate(hash) | ||
| for (index, byte):(Int, UInt8) in zip(block.indices, hash) | ||
| { | ||
| block[index] ^= byte | ||
| } | ||
| } | ||
|
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| output.append(contentsOf: block) | ||
| } | ||
| return output | ||
| } | ||
| } |
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