Audio Steganography¶
Hide secret messages or binary data within audio signals so that casual listeners hear only the original sound.
Three methods are provided:
Method |
Capacity |
Audibility |
Robustness |
Requirement |
|---|---|---|---|---|
LSB ( |
~1 bit/sample (~16 KB per 3 s at 44.1 kHz) |
Inaudible (≈ −90 dB) |
Fragile (destroyed by lossy compression) |
Any sample rate |
Frequency-band ( |
~2.6 kbit/s (~121 bytes per 3 s at 44.1 kHz) |
Above most listeners’ hearing range |
Moderate (survives mild noise) |
sample_rate ≥ 40 kHz |
Spectrogram text ( |
~1 bit/sample (same as LSB) |
Audible as buzzy tones; visually readable in spectrogram |
Fragile (same as LSB) |
Any sample rate |
All methods prepend a 32-bit length header so the decoder can recover the message without knowing its length in advance.
- pyminidsp.steg_capacity(signal_len, sample_rate, method=0)[source]¶
Compute maximum message length that can be hidden.
Compute the maximum message length (in bytes) that can be hidden.
- pyminidsp.steg_encode(host, message, sample_rate=44100.0, method=0)[source]¶
Encode a secret text message into a host audio signal.
- Parameters:
- Returns:
(stego_signal, num_bytes_encoded) tuple.
- Return type:
Encode a secret text message into a host audio signal.
LSB — flips the least-significant bit of a 16-bit PCM representation. Distortion ≈ −90 dB.
Frequency-band — adds a low-amplitude BFSK tone in the near-ultrasonic band (18.5 / 19.5 kHz).
Spectrogram text — hybrid LSB encoding that also renders the message as readable text in a spectrogram view.
- Parameters:
host (ArrayLike) – Host signal (not modified).
message (str) – String message to hide.
sample_rate (float) – Sample rate in Hz.
method (int) –
STEG_LSB,STEG_FREQ_BAND, orSTEG_SPECTEXT.
- Returns:
(stego_signal, num_bytes_encoded)tuple.- Return type:
host = md.sine_wave(44100, amplitude=0.8, freq=440.0, sample_rate=44100.0) stego, n = md.steg_encode(host, "secret", sample_rate=44100.0, method=md.STEG_LSB)
- pyminidsp.steg_decode(stego, sample_rate=44100.0, method=0, max_msg_len=4096)[source]¶
Decode a secret text message from a stego audio signal.
- Returns:
Decoded string message.
- Parameters:
- Return type:
Decode a secret text message from a stego audio signal.
- pyminidsp.steg_encode_bytes(host, data, sample_rate=44100.0, method=0)[source]¶
Encode arbitrary binary data into a host audio signal.
- Parameters:
- Returns:
(stego_signal, num_bytes_encoded) tuple.
- Return type:
Encode arbitrary binary data (may contain null bytes — e.g. images, compressed archives, cryptographic keys).
- pyminidsp.steg_decode_bytes(stego, sample_rate=44100.0, method=0, max_len=4096)[source]¶
Decode binary data from a stego audio signal.
- Returns:
bytes object containing the decoded data.
- Parameters:
- Return type:
Decode binary data from a stego audio signal.
- pyminidsp.steg_detect(signal, sample_rate=44100.0)[source]¶
Detect which steganography method was used.
- Returns:
(method, payload_type) tuple, or (None, None) if no steg detected. method is STEG_LSB, STEG_FREQ_BAND, or None. payload_type is STEG_TYPE_TEXT, STEG_TYPE_BINARY, or None.
- Parameters:
signal (ArrayLike)
sample_rate (float)
- Return type:
Detect which steganography method (if any) was used.
Probes the signal for a valid header using all three methods (LSB, frequency-band, and spectrogram text). If multiple appear valid, frequency-band is preferred (lower false-positive rate).