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ssh: use RSA/SHA-256 instead of RSA/SHA-1 as the public key algorithm

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openssh now disables RSA/SHA-1 by default, so using RSA/SHA-1 will
eventually cause us problems:

https://undeadly.org/cgi?action=article;sid=20210830113413

in addition, github will disable RSA/SHA-1 for recently added RSA keys:

https://github.blog/2021-09-01-improving-git-protocol-security-github/

this patch modifies ssh.c to use RSA/SHA-256 (aka rsa-sha2-256)
instead of RSA/SHA-1 (aka ssh-rsa) as the public key algorithm.

NOTE: public rsa keys and thumbprints are ***NOT AFFECTED***
by this patch.

while we're here, remove the workaround for github.com. it seems
that github has fixed their implementation, and does not look into
macalgs when we're using an aead cipher.
---
This commit is contained in:
kemal 2021-09-02 13:28:48 +00:00
parent 19a548fd49
commit 1a444750d6
1 changed files with 14 additions and 12 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

26
sys/src/cmd/ssh.c
View file

@ -398,14 +398,16 @@ ssh2rsapub(uchar *data, int len)
return pub;
}
static char rsasha256[] = "rsa-sha2-256";
int
rsasig2ssh(RSApub *pub, mpint *S, uchar *data, int len)
{
int l = (mpsignif(pub->n)+7)/8;
if(4+7+4+l > len)
if(4+12+4+l > len)
return -1;
mptober(S, data+4+7+4, l);
return pack(data, len, "ss", sshrsa, sizeof(sshrsa)-1, data+4+7+4, l);
mptober(S, data+4+12+4, l);
return pack(data, len, "ss", rsasha256, sizeof(rsasha256)-1, data+4+12+4, l);
}
mpint*
@ -417,7 +419,7 @@ ssh2rsasig(uchar *data, int len)
m = mpnew(0);
if(unpack(data, len, "sm", &s, &n, m) < 0
|| n != sizeof(sshrsa)-1 || memcmp(s, sshrsa, n) != 0){
|| n != sizeof(rsasha256)-1 || memcmp(s, rsasha256, n) != 0){
mpfree(m);
return nil;
}
@ -427,10 +429,10 @@ ssh2rsasig(uchar *data, int len)
mpint*
pkcs1digest(uchar *data, int len, RSApub *pub)
{
uchar digest[SHA1dlen], buf[256];
uchar digest[SHA2_256dlen], buf[256];
sha1(data, len, digest, nil);
return pkcs1padbuf(buf, asn1encodedigest(sha1, digest, buf, sizeof(buf)), pub->n, 1);
sha2_256(data, len, digest, nil);
return pkcs1padbuf(buf, asn1encodedigest(sha2_256, digest, buf, sizeof(buf)), pub->n, 1);
}
int
@ -489,7 +491,7 @@ kex(int gotkexinit)
static char kexalgs[] = "curve25519-sha256,curve25519-sha256@libssh.org";
static char cipheralgs[] = "chacha20-poly1305@openssh.com";
static char zipalgs[] = "none";
static char macalgs[] = "hmac-sha1"; /* work around for github.com */
static char macalgs[] = "";
static char langs[] = "";
uchar cookie[16], x[32], yc[32], z[32], k[32+1], h[SHA2_256dlen], *ys, *ks, *sig;
@ -506,7 +508,7 @@ kex(int gotkexinit)
sendpkt("b[ssssssssssbu", MSG_KEXINIT,
cookie, sizeof(cookie),
kexalgs, sizeof(kexalgs)-1,
sshrsa, sizeof(sshrsa)-1,
rsasha256, sizeof(rsasha256)-1,
cipheralgs, sizeof(cipheralgs)-1,
cipheralgs, sizeof(cipheralgs)-1,
macalgs, sizeof(macalgs)-1,
@ -744,7 +746,7 @@ pubkeyauth(void)
service, strlen(service),
authmeth, sizeof(authmeth)-1,
0,
sshrsa, sizeof(sshrsa)-1,
rsasha256, sizeof(rsasha256)-1,
pk, npk);
Next1: switch(recvpkt()){
default:
@ -767,7 +769,7 @@ Next1: switch(recvpkt()){
service, strlen(service),
authmeth, sizeof(authmeth)-1,
1,
sshrsa, sizeof(sshrsa)-1,
rsasha256, sizeof(rsasha256)-1,
pk, npk);
S = pkcs1digest(send.b, n, pub);
n = snprint((char*)send.b, sizeof(send.b), "%B", S);
@ -788,7 +790,7 @@ Next1: switch(recvpkt()){
service, strlen(service),
authmeth, sizeof(authmeth)-1,
1,
sshrsa, sizeof(sshrsa)-1,
rsasha256, sizeof(rsasha256)-1,
pk, npk,
sig, nsig);
Next2: switch(recvpkt()){