Dear,
I would like to recommend change/extend support of algorithms for DKIM
signage. Last update of algorithms are in RFC 8463, still not widely
supported. Right now we facing issues with the long DKIM key
distribution and lack of support, allowing the ECC signature can solve
problem with key size.
Elliptic curve signatures:
I would like to recommend not only Ed25519, but also Ed448. Thanks to
clever design, signatures based on on that algorithms can avoid of nonce
collisions. But this could be real risk for the DSS standard curve
implementation.
| Key size | Curve | Nonce | Security Equivalent
| Hash |
----------+----------+-----------------+----------+---------------------+----------+
Ed25519 | 255b | Twisted Edwards | Text+Key | 125b | SHA256 |
Ed448 | 448b | Twisted Edwards | Text+Key | 224b | SHAKE256 |
NIST P256 | 256b | Weierstrass | Random | 128b | SHA256 |
NIST P384 | 384b | Weierstrass | Random | 192b | SHA384 |
NIST P521 | 521b | Weierstrass | Random | 230b | SHA512 |
RSA signatures:
But the RSA signature, require extremely long private keys. To assure
similar security equivalent, need to be at the least 12 times longer.
But RSA have sub-exponential complexity.
Key size | Security Equivalent |
---------+---------------------+
1024b | 96b |
2048b | 112b |
3072b | 128b |
4096b | 160b |
The signature based on RSA has some issues, but based on key properties
nobody will be able to decide between them. In case of change required,
need to be mentioned i DKIM key. Use of k=rsa for PKCS#1 v 1.5 as
default value or k=rsa-pss for PKCS#1 v 2.2 RSA-PSS are probably the
only solution.
PKCS#1 v 1.0, obsolete, has not been supported
PKCS#1 v 1.5, obsolete, vulnerable by Bleichenbacher family of attacks
PKCS#1 v 2.2 RSA-PSS (DSS standard), described in NIST FIPS 186-5
Support:
EU directive eIDAS and ETSI standard ETSI TS 119312 support signatures
based on RSA PKCS#1 v 1.5, RSA-PSS, ED25519, ED448, NIST P-256, NIST
P-384, NIST P-521
NIST FIPS 186-5 support signatures based on RSA PKCS#1 v 1.5, RSA-PSS,
ED25519, ED448, NIST P-256, NIST P-384, NIST P-521
RFC 8446 TLS 1.3 support signatures based on RSA PKCS#1 v 1.5, RSA-PSS,
ED25519, ED448, NIST P-256, NIST P-384, NIST P-521
Regards
Jan
--
-- --- ----- -
Jan Dušátko
Tracker number: +420 602 427 840
e-mail: j...@dusatko.org
GPG Signature: https://keys.dusatko.org/E535B585.asc
GPG Encrypt: https://keys.dusatko.org/B76A1587.asc
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