Achim Hügen created SSHD-1107:
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Summary: Diffie Hellmann group exchange minimum key size should be
configurable for security reasons
Key: SSHD-1107
URL: https://issues.apache.org/jira/browse/SSHD-1107
Project: MINA SSHD
Issue Type: Bug
Affects Versions: 2.5.1
Reporter: Achim Hügen
Currently the minimum key size for DH group exchange is 1024 bit (for example
when using diffie-hellman-group-exchange-sha256 for KEX)
This is below the current recommendations of 2048 bit (see
[NIST|https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-57Pt3r1.pdf],
Table 2-1 and
[https://tools.ietf.org/id/draft-ietf-curdle-ssh-kex-sha2-09.html#rfc.section.3.4).]
For compatibility reasons it is still essential to support
diffie-hellman-group-exchange-sha256, but the minimum key size should be
configurable, so that a server operator can harden its server.
The minimum size is hardcoded in
org.apache.sshd.common.util.security.SecurityUtils#MIN_DHGEX_KEY_SIZE
This could be made configurable via a system property like one already exists
for the maximum (see MAX_DHGEX_KEY_SIZE_PROP)
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