Commit 81491991 authored by Niels Möller's avatar Niels Möller

Describe RSA improvements in NEWS.

parent 6487ef7e
NEWS for the Nettle 3.4.1 release
This is a bugfix release.
This release fixes a few bugs, and makes the RSA private key
operations side channel silent. The RSA improvements are
contributed by Simo Sorce and Red Hat, and includes one new
public function.
All functions handling RSA private keys are now side-channel
silent, meaning that they try hard to avoid any branches or
memory accesses depending on secret data. This applies both to
the bignum calculations, which now use GMP's mpn_sec_* family
of functions, and the processing of pkcs#1 padding.
Nettle's ECC functions were already side-channel silent, while
the DSA functions still aren't. There's also one caveat
regarding the improved RSA functions: due to small table
lookups in relevant mpn_sec_* functions in GMP-6.1.2, the
lowest and highest few bits of the secret factors p and q may
leak. I'm not aware of any attacks on RSA where knowing a few
bits of the factors makes a significant difference. This leak
will likely be plugged in later GMP versions).
Changes in behavior:
* The old rsa_decrypt_tr may now clobber all of the provided
message buffer, independent of the actual message length. It
is side-channel silent, in that branches and memory accesses
don't depend on the validity or length of the message.
Side-channel leakage from the caller's use of length and
return value may still provide an oracle useable for a
Bleichenbacher-style chosen ciphertext attack. Which is why
the new function rsa_sec_decrypt, see below, is recommended.
New features:
* New function rsa_sec_decrypt. It differs from rsa_decrypt_tr
in that the length of the decrypted message is given a
priori, and pkcs#1 padding indicating a different length is
treated as an error. For applications that may be subject to
chosen ciphertext attacks, it is recommended to initialize
the message area with random data, call this function, and
ignore the return value. This applies in particular to
RSA-based key exchange in the TLS protocol.
Bug fixes:
......@@ -138,7 +178,7 @@ NEWS for the Nettle 3.3 release
This release fixes a couple of bugs, and improves resistance
to side-channel attacks on RSA and DSA private key operations.
Changes in behavoir:
Changes in behavior:
* Invalid private RSA keys, with an even modulo, are now
rejected by rsa_private_key_prepare. (Earlier versions
......
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