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Ayke van Laethem
d3863f337d
The crypto/rand package is used for sensitive cryptographic operations. Do not use the rp2040 RNG for this purpose, because it's not strong enough for cryptography. I think it is _possible_ to make use of the RP2040 RNG to create cryptographically secure pseudo-random numbers, but it needs some entropy calculation and secure hashing (blake2s or so) to make them truly unpredictable.
43 lines
969 B
Go
43 lines
969 B
Go
//go:build rp2040
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// +build rp2040
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// Implementation based on code located here:
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// https://github.com/raspberrypi/pico-sdk/blob/master/src/rp2_common/pico_lwip/random.c
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package machine
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import (
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"device/rp"
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)
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const numberOfCycles = 32
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// GetRNG returns 32 bits of semi-random data based on ring oscillator.
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//
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// Unlike some other implementations of GetRNG, these random numbers are not
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// cryptographically secure and must not be used for cryptographic operations
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// (nonces, etc).
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func GetRNG() (uint32, error) {
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var val uint32
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for i := 0; i < 4; i++ {
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val = (val << 8) | uint32(roscRandByte())
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}
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return val, nil
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}
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var randomByte uint8
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func roscRandByte() uint8 {
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var poly uint8
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for i := 0; i < numberOfCycles; i++ {
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if randomByte&0x80 != 0 {
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poly = 0x35
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} else {
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poly = 0
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}
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randomByte = ((randomByte << 1) | uint8(rp.ROSC.GetRANDOMBIT()) ^ poly)
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// TODO: delay a little because the random bit is a little slow
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}
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return randomByte
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}
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