aescry 1.0.0

AES encryption and decryption, including the AES Crypt file format.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282

mod common;

use aescry::aescrypt::{self, Decryptor, Encryptor, Extension, Iterations, Limits};
use aescry::{detect, Error, Limit, StreamError, Version};
use std::io::{self, Read};
use std::path::PathBuf;

const PASSWORD: &str = "aescry test ✓";
const FOX: &[u8] = b"The quick brown fox jumps over the lazy dog\n";

fn fixture(name: &str) -> Vec<u8> {
    let path = PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("tests/data/aescrypt").join(name);
    std::fs::read(&path).unwrap_or_else(|e| panic!("{}: {}", path.display(), e))
}

fn fast(password: &str) -> Encryptor {
    Encryptor::new(password).unwrap().iterations(Iterations::new(1000).unwrap())
}

#[test]
fn decrypts_fixtures_of_every_version() {
    for (v, version) in [(0, Version::V0), (1, Version::V1), (2, Version::V2), (3, Version::V3)] {
        let fox = fixture(&format!("fox.v{}.aes", v));
        let empty = fixture(&format!("empty.v{}.aes", v));

        assert_eq!(detect::from_bytes(&fox), Some(version));
        assert_eq!(detect::from_bytes(&empty), Some(version));

        assert_eq!(aescrypt::decrypt(PASSWORD, &fox).unwrap(), FOX, "fox v{}", v);
        assert_eq!(aescrypt::decrypt(PASSWORD, &empty).unwrap(), b"", "empty v{}", v);

        assert!(matches!(aescrypt::decrypt("aescry test", &fox), Err(Error::InvalidPassword)), "v{}", v);
    }

    // the smallest streams of versions 0-2 are exactly the documented minimum
    for v in [Version::V0, Version::V1, Version::V2] {
        assert_eq!(fixture(&format!("empty.v{}.aes", v.as_u8())).len(), v.min_stream_len());
    }
}

#[test]
fn roundtrip_many_sizes() {
    let enc = fast("pw");
    let dec = Decryptor::new("pw").unwrap();

    for len in [0, 1, 15, 16, 17, 31, 32, 33, 1000, 65535, 65536, 65537, 70000] {
        let data: Vec<u8> = (0..len).map(|i| (i * 31 + 7) as u8).collect();
        let encrypted = enc.encrypt(&data).unwrap();

        assert_eq!(detect::from_bytes(&encrypted), Some(Version::V3));
        // header + key block + HMACs + PKCS#7 padded ciphertext
        let header = aescrypt::read_header(&encrypted[..]).unwrap();
        assert_eq!(encrypted.len(), header.len() + 48 + 32 + (len / 16 + 1) * 16 + 32);

        assert_eq!(dec.decrypt(&encrypted).unwrap(), data, "length {}", len);
    }
}

#[test]
fn every_encryption_is_different() {
    let a = fast("pw").encrypt(b"same").unwrap();
    let b = fast("pw").encrypt(b"same").unwrap();
    assert_ne!(a, b);
}

#[test]
fn header_contents() {
    let encrypted = fast("pw")
        .extension(Extension::new("urn:example:note", "hello").unwrap())
        .encrypt(b"x")
        .unwrap();

    let header = aescrypt::read_header(&encrypted[..]).unwrap();
    assert_eq!(header.version(), Version::V3);
    assert_eq!(header.iterations(), Some(1000));
    assert_eq!(header.reserved(), 0);
    let created_by = format!("aescry {}", env!("CARGO_PKG_VERSION"));
    assert_eq!(header.extension("CREATED_BY"), Some(created_by.as_bytes()));
    assert_eq!(header.extension("urn:example:note"), Some(&b"hello"[..]));

    let exts = header.extensions();
    assert_eq!(exts.len(), 3);
    assert!(exts[2].is_container());
    assert_eq!(exts[2].as_bytes().len(), 128);

    let bare = fast("pw").without_default_extensions().encrypt(b"x").unwrap();
    assert!(aescrypt::read_header(&bare[..]).unwrap().extensions().is_empty());
    assert_eq!(bare.len(), 155 + 16 - 16); // minimum stream: one padded block
}

#[test]
fn rejects_bad_parameters() {
    assert!(matches!(Encryptor::new(""), Err(Error::EmptyPassword)));
    assert!(matches!(Decryptor::new(""), Err(Error::EmptyPassword)));
    assert!(matches!(aescrypt::encrypt("", b"x"), Err(Error::EmptyPassword)));

    // iteration counts are checked when the value is created
    assert!(matches!(Iterations::new(0), Err(Error::InvalidIterations(0))));
    assert!(matches!(Iterations::new(5_000_001), Err(Error::InvalidIterations(5_000_001))));
    assert!(Iterations::try_from(5_000_000u32).is_ok());
}

#[test]
fn refuses_excessive_iterations_in_a_stream() {
    let mut encrypted = fast("pw").without_default_extensions().encrypt(b"x").unwrap();
    // iterations follow "AES", version, reserved and the empty extension list
    encrypted[7..11].copy_from_slice(&5_000_001u32.to_be_bytes());
    assert!(matches!(
        aescrypt::decrypt("pw", &encrypted),
        Err(Error::LimitExceeded(Limit::Iterations { found: 5_000_001, max: 5_000_000 }))
    ));

    encrypted[7..11].copy_from_slice(&0u32.to_be_bytes());
    assert!(matches!(aescrypt::decrypt("pw", &encrypted), Err(Error::InvalidStream(StreamError::ZeroIterations))));

    let encrypted = fast("pw").encrypt(b"x").unwrap();
    let strict = Decryptor::new("pw").unwrap().limits(Limits::DEFAULT.max_iterations(999));
    assert!(matches!(
        strict.decrypt(&encrypted),
        Err(Error::LimitExceeded(Limit::Iterations { found: 1000, max: 999 }))
    ));

    // the normal API cannot raise limits above the defaults
    encrypted_with(5_000_001);
    fn encrypted_with(n: u32) {
        let lenient = Decryptor::new("pw").unwrap().limits(Limits::DEFAULT.max_iterations(u32::MAX));
        let mut stream = fast("pw").without_default_extensions().encrypt(b"x").unwrap();
        stream[7..11].copy_from_slice(&n.to_be_bytes());
        assert!(matches!(lenient.decrypt(&stream), Err(Error::LimitExceeded(Limit::Iterations { .. }))));
    }
}

#[test]
fn detects_tampering_everywhere() {
    let encrypted = fast("pw").without_default_extensions().encrypt(&[0x42; 40]).unwrap();
    let header_len = aescrypt::read_header(&encrypted[..]).unwrap().len();
    let key_block = header_len..header_len + 80;

    for i in 0..encrypted.len() {
        let mut altered = encrypted.clone();
        altered[i] ^= 0x01;

        let result = aescrypt::decrypt("pw", &altered);

        if i == 4 {
            // the reserved octet is not covered by either HMAC, and AES Crypt
            // ignores it when reading
            assert!(result.is_ok());
            continue;
        }

        assert!(result.is_err(), "flipping octet {} was not detected", i);

        if i >= 11 && i < header_len {
            // the public IV feeds key derivation, so the key HMAC fails
            assert!(matches!(result, Err(Error::InvalidPassword)), "octet {}: {:?}", i, result);
        } else if key_block.contains(&i) {
            assert!(matches!(result, Err(Error::InvalidPassword)), "octet {}: {:?}", i, result);
        } else if i >= key_block.end {
            assert!(matches!(result, Err(Error::AlteredMessage)), "octet {}: {:?}", i, result);
        }
    }

    for len in 0..encrypted.len() {
        assert!(aescrypt::decrypt("pw", &encrypted[..len]).is_err(), "truncated to {}", len);
    }

    let mut extended = encrypted.clone();
    extended.push(0);
    assert!(aescrypt::decrypt("pw", &extended).is_err());
}

#[test]
fn extensions_are_not_authenticated() {
    // documented behavior: extensions can change without failing decryption
    let mut encrypted = fast("pw").encrypt(b"data").unwrap();
    let pos = encrypted.windows(6).position(|w| w == b"aescry").unwrap();
    encrypted[pos] = b'X';
    assert_eq!(aescrypt::decrypt("pw", &encrypted).unwrap(), b"data");
}

#[test]
fn not_aes_crypt() {
    assert!(matches!(aescrypt::decrypt("pw", b"hello world"), Err(Error::NotAesCrypt)));
    assert!(matches!(aescrypt::decrypt("pw", b"AES\x04\x00"), Err(Error::UnsupportedVersion(4))));
    assert!(matches!(aescrypt::decrypt("pw", b"AES"), Err(Error::InvalidStream(_))));
    assert!(matches!(aescrypt::decrypt("pw", b""), Err(Error::InvalidStream(_))));
}

/// A reader that returns at most `n` octets per read.
struct Trickle<'a> {
    data: &'a [u8],
    n: usize,
}

impl Read for Trickle<'_> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        let n = self.n.min(buf.len()).min(self.data.len());
        buf[..n].copy_from_slice(&self.data[..n]);
        self.data = &self.data[n..];
        Ok(n)
    }
}

#[test]
fn streams_with_small_reads() {
    let data: Vec<u8> = (0..70_000u32).map(|i| (i % 251) as u8).collect();

    for n in [1, 7, 16, 33, 4096] {
        let mut encrypted = Vec::new();
        let read = fast("pw").encrypt_stream(Trickle { data: &data, n }, &mut encrypted).unwrap();
        assert_eq!(read, data.len() as u64);

        let mut decrypted = Vec::new();
        let written = Decryptor::new("pw")
            .unwrap()
            .decrypt_stream(Trickle { data: &encrypted, n }, &mut decrypted)
            .unwrap();

        assert_eq!(written, data.len() as u64);
        assert_eq!(decrypted, data, "read size {}", n);
    }
}

#[test]
fn files() {
    let dir = std::env::temp_dir().join(format!("aescry-files-{}", std::process::id()));
    std::fs::create_dir_all(&dir).unwrap();

    let plain = dir.join("plain.bin");
    let encrypted = dir.join("plain.bin.aes");
    let decrypted = dir.join("decrypted.bin");
    std::fs::write(&plain, FOX).unwrap();

    assert_eq!(fast("pw").encrypt_file(&plain, &encrypted).unwrap(), FOX.len() as u64);
    assert_eq!(detect::get_file(&encrypted).unwrap().version(), Version::V3);

    let dec = Decryptor::new("pw").unwrap();
    assert_eq!(dec.decrypt_file(&encrypted, &decrypted).unwrap(), FOX.len() as u64);
    assert_eq!(std::fs::read(&decrypted).unwrap(), FOX);

    // a failed decryption leaves no output behind
    let missing = dir.join("never-created.bin");
    let wrong = Decryptor::new("wrong").unwrap();
    assert!(matches!(wrong.decrypt_file(&encrypted, &missing), Err(Error::InvalidPassword)));
    assert!(!missing.exists());

    // ...and does not replace an existing file
    std::fs::write(&decrypted, b"keep me").unwrap();
    assert!(wrong.decrypt_file(&encrypted, &decrypted).is_err());
    assert_eq!(std::fs::read(&decrypted).unwrap(), b"keep me");

    let leftovers: Vec<_> = std::fs::read_dir(&dir)
        .unwrap()
        .filter_map(|e| e.ok())
        .filter(|e| e.file_name().to_string_lossy().contains("aescry-tmp"))
        .collect();
    assert!(leftovers.is_empty());

    assert!(matches!(dec.decrypt_file(dir.join("nope.aes"), &decrypted), Err(Error::Io(_))));

    std::fs::remove_dir_all(&dir).unwrap();
}

#[test]
fn require_constant_time() {
    let ct = aescry::aes::Backend::constant_time();
    let enc = fast("pw").require_constant_time().encrypt(b"x");
    let dec = Decryptor::new("pw").unwrap().require_constant_time();

    match ct {
        Ok(backend) => {
            assert!(backend.is_constant_time());
            assert_eq!(dec.decrypt(&enc.unwrap()).unwrap(), b"x");
        }
        Err(_) => {
            assert!(matches!(enc, Err(Error::BackendUnavailable)));
            let stream = fast("pw").encrypt(b"x").unwrap();
            assert!(matches!(dec.decrypt(&stream), Err(Error::BackendUnavailable)));
        }
    }
}