9front - general discussion about 9front
 help / color / mirror / Atom feed
* [9front] ssh: use RSA/SHA-256 instead of RSA/SHA-1 as the public key algorithm
@ 2021-09-01  0:22 kemal
  2021-09-02 13:33 ` [9front] " kemal
  0 siblings, 1 reply; 3+ messages in thread
From: kemal @ 2021-09-01  0:22 UTC (permalink / raw)
  To: 9front

[-- Attachment #1: Type: text/plain, Size: 380 bytes --]

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

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.

patch attached.

[-- Attachment #2: patch.txt --]
[-- Type: text/plain, Size: 2924 bytes --]

From: kemal <kemalinanc8@gmail.com>
Date: Wed, 01 Sep 2021 00:13:21 +0000
Subject: [PATCH] ssh: use RSA/SHA-256 instead of RSA/SHA-1 as the public key algorithm


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

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.
---
diff 6c9462710539bd35ae5c51de27e7894522683bd7 44b3808acb09cbc39f4fdac2f285f7efa62cd0d0
--- a/sys/src/cmd/ssh.c	Tue Aug 31 18:53:37 2021
+++ b/sys/src/cmd/ssh.c	Wed Sep  1 03:13:21 2021
@@ -373,6 +373,7 @@
 }
 
 static char sshrsa[] = "ssh-rsa";
+static char rsasha2_256[] = "rsa-sha2-256";
 
 int
 rsapub2ssh(RSApub *rsa, uchar *data, int len)
@@ -402,10 +403,10 @@
 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", rsasha2_256, sizeof(rsasha2_256)-1, data+4+12+4, l);
 }
 
 mpint*
@@ -417,7 +418,7 @@
 
 	m = mpnew(0);
 	if(unpack(data, len, "sm", &s, &n, m) < 0
-	|| n != sizeof(sshrsa)-1 || memcmp(s, sshrsa, n) != 0){
+	|| n != sizeof(rsasha2_256)-1 || memcmp(s, rsasha2_256, n) != 0){
 		mpfree(m);
 		return nil;
 	}
@@ -427,10 +428,10 @@
 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
@@ -506,7 +507,7 @@
 	sendpkt("b[ssssssssssbu", MSG_KEXINIT,
 		cookie, sizeof(cookie),
 		kexalgs, sizeof(kexalgs)-1,
-		sshrsa, sizeof(sshrsa)-1,
+		rsasha2_256, sizeof(rsasha2_256)-1,
 		cipheralgs, sizeof(cipheralgs)-1,
 		cipheralgs, sizeof(cipheralgs)-1,
 		macalgs, sizeof(macalgs)-1,
@@ -744,7 +745,7 @@
 			service, strlen(service),
 			authmeth, sizeof(authmeth)-1,
 			0,
-			sshrsa, sizeof(sshrsa)-1,
+			rsasha2_256, sizeof(rsasha2_256)-1,
 			pk, npk);
 Next1:		switch(recvpkt()){
 		default:
@@ -767,7 +768,7 @@
 			service, strlen(service),
 			authmeth, sizeof(authmeth)-1,
 			1,
-			sshrsa, sizeof(sshrsa)-1,
+			rsasha2_256, sizeof(rsasha2_256)-1,
 			pk, npk);
 		S = pkcs1digest(send.b, n, pub);
 		n = snprint((char*)send.b, sizeof(send.b), "%B", S);
@@ -788,7 +789,7 @@
 			service, strlen(service),
 			authmeth, sizeof(authmeth)-1,
 			1,
-			sshrsa, sizeof(sshrsa)-1,
+			rsasha2_256, sizeof(rsasha2_256)-1,
 			pk, npk,
 			sig, nsig);
 Next2:		switch(recvpkt()){

^ permalink raw reply	[flat|nested] 3+ messages in thread

* [9front] Re: ssh: use RSA/SHA-256 instead of RSA/SHA-1 as the public key algorithm
  2021-09-01  0:22 [9front] ssh: use RSA/SHA-256 instead of RSA/SHA-1 as the public key algorithm kemal
@ 2021-09-02 13:33 ` kemal
  2021-09-02 15:49   ` cinap_lenrek
  0 siblings, 1 reply; 3+ messages in thread
From: kemal @ 2021-09-02 13:33 UTC (permalink / raw)
  To: 9front

[-- Attachment #1: Type: text/plain, Size: 169 bytes --]

> patch attached.

i have seen that github does not require the "hmac-sha1" workaround
any more. i removed it. and i cleaned up the patch a bit.

new patch is attached.

[-- Attachment #2: patch.txt --]
[-- Type: text/plain, Size: 3537 bytes --]

From: kemal <kemalinanc8@gmail.com>
Date: Thu, 02 Sep 2021 13:28:48 +0000
Subject: [PATCH] ssh: use RSA/SHA-256 instead of RSA/SHA-1 as the public key algorithm


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.
---
diff 6c9462710539bd35ae5c51de27e7894522683bd7 696ce28faddb131842825b0bedb8caa6d1a9ec62
--- a/sys/src/cmd/ssh.c	Tue Aug 31 18:53:37 2021
+++ b/sys/src/cmd/ssh.c	Thu Sep  2 16:28:48 2021
@@ -398,14 +398,16 @@
 	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 @@
 
 	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 @@
 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 @@
 	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 @@
 	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 @@
 			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 @@
 			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 @@
 			service, strlen(service),
 			authmeth, sizeof(authmeth)-1,
 			1,
-			sshrsa, sizeof(sshrsa)-1,
+			rsasha256, sizeof(rsasha256)-1,
 			pk, npk,
 			sig, nsig);
 Next2:		switch(recvpkt()){

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [9front] Re: ssh: use RSA/SHA-256 instead of RSA/SHA-1 as the public key algorithm
  2021-09-02 13:33 ` [9front] " kemal
@ 2021-09-02 15:49   ` cinap_lenrek
  0 siblings, 0 replies; 3+ messages in thread
From: cinap_lenrek @ 2021-09-02 15:49 UTC (permalink / raw)
  To: 9front

applied, thanks!

--
cinap

^ permalink raw reply	[flat|nested] 3+ messages in thread

end of thread, other threads:[~2021-09-02 15:57 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-09-01  0:22 [9front] ssh: use RSA/SHA-256 instead of RSA/SHA-1 as the public key algorithm kemal
2021-09-02 13:33 ` [9front] " kemal
2021-09-02 15:49   ` cinap_lenrek

9front - general discussion about 9front

This inbox may be cloned and mirrored by anyone:

	git clone --mirror https://inbox.vuxu.org/9front

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V1 9front 9front/ https://inbox.vuxu.org/9front \
		9front@9front.org
	public-inbox-index 9front

Example config snippet for mirrors.
Newsgroup available over NNTP:
	nntp://inbox.vuxu.org/vuxu.archive.9front


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git