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Update SECURITY.md

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Signed-off-by: Ronald Cron <ronald.cron@arm.com>
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Ronald Cron
2025-09-30 12:19:29 +02:00
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SECURITY.md
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@@ -37,10 +37,6 @@ being implemented. (For example Mbed TLS alone won't guarantee that the
messages will arrive without delay, as the TLS protocol doesn't guarantee that
either.)
**Warning!** Block ciphers do not yet achieve full protection against attackers
who can measure the timing of packets with sufficient precision. For details
and workarounds see the [Block Ciphers](#block-ciphers) section.
### Local attacks
In this section, we consider an attacker who can run software on the same
@@ -69,9 +65,6 @@ physical side channels as well. Remote and physical timing attacks are covered
in the [Remote attacks](remote-attacks) and [Physical
attacks](physical-attacks) sections respectively.
**Warning!** Block ciphers do not yet achieve full protection. For
details and workarounds see the [Block Ciphers](#block-ciphers) section.
#### Local non-timing side channels
The attacker code running on the platform has access to some sensor capable of
@@ -115,36 +108,6 @@ protection against a class of attacks outside of the above described threat
model. Neither does it mean that the failure of such a countermeasure is
considered a vulnerability.
#### Block ciphers
Currently there are four block ciphers in Mbed TLS: AES, CAMELLIA, ARIA and
DES. The pure software implementation in Mbed TLS implementation uses lookup
tables, which are vulnerable to timing attacks.
These timing attacks can be physical, local or depending on network latency
even a remote. The attacks can result in key recovery.
**Workarounds:**
- Turn on hardware acceleration for AES. This is supported only on selected
architectures and currently only available for AES. See configuration options
`MBEDTLS_AESCE_C`, `MBEDTLS_AESNI_C` for details.
- Add a secure alternative implementation (typically hardware acceleration) for
the vulnerable cipher. See the [Alternative Implementations
Guide](docs/architecture/alternative-implementations.md) for more information.
- Use cryptographic mechanisms that are not based on block ciphers. In
particular, for authenticated encryption, use ChaCha20/Poly1305 instead of
block cipher modes. For random generation, use HMAC\_DRBG instead of CTR\_DRBG.
#### Everest
The HACL* implementation of X25519 taken from the Everest project only protects
against remote timing attacks. (See their [Security
Policy](https://github.com/hacl-star/hacl-star/blob/main/SECURITY.md).)
The Everest variant is only used when `MBEDTLS_ECDH_VARIANT_EVEREST_ENABLED`
configuration option is defined. This option is off by default.
#### Formatting of X.509 certificates and certificate signing requests
When parsing X.509 certificates and certificate signing requests (CSRs),