[ptxdist] [PATCH 6/8] dropbear: Rework key exchange algorithm options

[Alexander Dahl <ada@thorsis.com>]

The options for diffie-hellman key exchange were mixed up with message
integrity hmacs.

Signed-off-by: Alexander Dahl <ada@thorsis.com>
---
 rules/dropbear.in   | 43 +++++++++++++++++++++++++++++++++++++++++--
 rules/dropbear.make | 36 ++++++++++++++++++++++++++++++++----
 2 files changed, 73 insertions(+), 6 deletions(-)

diff --git a/rules/dropbear.in b/rules/dropbear.in
index f7f96a762..043b0e76d 100644
--- a/rules/dropbear.in
+++ b/rules/dropbear.in
@@ -278,23 +278,62 @@ config DROPBEAR_ED25519
 	  Public keys are 256 bits long and signatures are 512 bits
 	  long.
 
-comment "Key exchange algorithm ---"
+comment "Key exchange algorithm, at least one required ---"
+
+config DROPBEAR_DH_GROUP14_SHA256
+	bool
+	prompt "group14_sha256"
+	default y
+	help
+	  2048 bit, sha2-256.
+	  group14 is supported by most implementations.
+
+config DROPBEAR_DH_GROUP14_SHA1
+	bool
+	prompt "group14_sha1"
+	help
+	  2048 bit, sha1.
+	  group14 is supported by most implementations.
+
+config DROPBEAR_DH_GROUP16
+	bool
+	prompt "group16"
+	help
+	  4096 bit, sha2-512.
+	  group16 provides a greater strength level but is slower and
+	  increases binary size.
 
 config DROPBEAR_ECDH
 	bool
 	prompt "ecdh"
 	help
 	  ECDH stands for Elliptic Curve Diffie-Hellman.
+	  
+	  Small systems should generally include either curve25519 or
+	  ecdh for performance.
 
 config DROPBEAR_CURVE25519
 	bool
-	prompt "curve25519-donna"
+	prompt "curve25519"
 	help
 	  Enable curve25519-donna for key exchange.
 	  This is another elliptic curve method with good security properties.
 	  This algorithm does not rely on NIST-based curves
 	  and gives us more security confidence against a possible
 	  backdoor in nistp-256 curve.
+	  
+	  Small systems should generally include either curve25519 or
+	  ecdh for performance.
+
+config DROPBEAR_DH_GROUP1
+	bool
+	prompt "group1 (legacy, client only)"
+	help
+	  1024 bit, sha1.
+	  is too small for security though is necessary if you need
+	  compatibility with some implementations such as Dropbear
+	  versions < 0.53.
+	  Client only!
 
 comment "Authentication types, at least one required --- RFC Draft requires pubkey auth"
 
diff --git a/rules/dropbear.make b/rules/dropbear.make
index 7653cf3e5..e86b8bf43 100644
--- a/rules/dropbear.make
+++ b/rules/dropbear.make
@@ -157,13 +157,9 @@ endif
 ifdef PTXCONF_DROPBEAR_SHA1
 	@echo "ptxdist: enabling sha1"
 	@echo "#define DROPBEAR_SHA1_HMAC 1" >> $(DROPBEAR_LOCALOPTIONS)
-	@echo "#define DROPBEAR_DH_GROUP1 1" >> $(DROPBEAR_LOCALOPTIONS)
-	@echo "#define DROPBEAR_DH_GROUP14_SHA1 1" >> $(DROPBEAR_LOCALOPTIONS)
 else
 	@echo "ptxdist: disabling sha1"
 	@echo "#define DROPBEAR_SHA1_HMAC 0" >> $(DROPBEAR_LOCALOPTIONS)
-	@echo "#define DROPBEAR_DH_GROUP1 0" >> $(DROPBEAR_LOCALOPTIONS)
-	@echo "#define DROPBEAR_DH_GROUP14_SHA1 0" >> $(DROPBEAR_LOCALOPTIONS)
 endif
 
 ifdef PTXCONF_DROPBEAR_SHA1_96
@@ -223,6 +219,30 @@ endif
 	@echo "#define DROPBEAR_SK_ED25519 0" >> $(DROPBEAR_LOCALOPTIONS)
 
 # key exchange algorithm
+ifdef PTXCONF_DROPBEAR_DH_GROUP14_SHA256
+	@echo "ptxdist: enabling dh_group14_sha256"
+	@echo "#define DROPBEAR_DH_GROUP14_SHA256 1" >> $(DROPBEAR_LOCALOPTIONS)
+else
+	@echo "ptxdist: disabling dh_group14_sha256"
+	@echo "#define DROPBEAR_DH_GROUP14_SHA256 0" >> $(DROPBEAR_LOCALOPTIONS)
+endif
+
+ifdef PTXCONF_DROPBEAR_DH_GROUP14_SHA1
+	@echo "ptxdist: enabling dh_group14_sha1"
+	@echo "#define DROPBEAR_DH_GROUP14_SHA1 1" >> $(DROPBEAR_LOCALOPTIONS)
+else
+	@echo "ptxdist: disabling dh_group14_sha1"
+	@echo "#define DROPBEAR_DH_GROUP14_SHA1 0" >> $(DROPBEAR_LOCALOPTIONS)
+endif
+
+ifdef PTXCONF_DROPBEAR_DH_GROUP16
+	@echo "ptxdist: enabling dh_group16"
+	@echo "#define DROPBEAR_DH_GROUP16 1" >> $(DROPBEAR_LOCALOPTIONS)
+else
+	@echo "ptxdist: disabling dh_group16"
+	@echo "#define DROPBEAR_DH_GROUP16 0" >> $(DROPBEAR_LOCALOPTIONS)
+endif
+
 ifdef PTXCONF_DROPBEAR_ECDH
 	@echo "ptxdist: enabling ecdh"
 	@echo "#define DROPBEAR_ECDH 1" >> $(DROPBEAR_LOCALOPTIONS)
@@ -239,6 +259,14 @@ else
 	@echo "#define DROPBEAR_CURVE25519 0" >> $(DROPBEAR_LOCALOPTIONS)
 endif
 
+ifdef PTXCONF_DROPBEAR_DH_GROUP1
+	@echo "ptxdist: enabling dh_group1"
+	@echo "#define DROPBEAR_DH_GROUP1 1" >> $(DROPBEAR_LOCALOPTIONS)
+else
+	@echo "ptxdist: disabling dh_group1"
+	@echo "#define DROPBEAR_DH_GROUP1 0" >> $(DROPBEAR_LOCALOPTIONS)
+endif
+
 # authentication types
 ifdef PTXCONF_DROPBEAR_PASSWD
 	@echo "ptxdist: enabling passwd"
-- 
2.30.2