Phase 1 of SHA256 support

- new variable "digestalg" which defaults to "sha1", but allows "sha256"
  for those who want to sign using this
- Addresses #953

src/highlevelcrypto.py

@@ -1,4 +1,5 @@
 from binascii import hexlify
+from bmconfigparser import BMConfigParser
 import pyelliptic
 from pyelliptic import arithmetic as a, OpenSSL
 def makeCryptor(privkey):
@@ -35,8 +36,17 @@ def sign(msg,hexPrivkey):
     # upgrade PyBitmessage gracefully. 
     # https://github.com/yann2192/pyelliptic/pull/33
     # More discussion: https://github.com/yann2192/pyelliptic/issues/32
-    return makeCryptor(hexPrivkey).sign(msg, digest_alg=OpenSSL.digest_ecdsa_sha1) # SHA1
-    #return makeCryptor(hexPrivkey).sign(msg, digest_alg=OpenSSL.EVP_sha256) # SHA256. We should switch to this eventually.
+    digestAlg = BMConfigParser().safeGet('bitmessagesettings', 'digestalg', 'sha1')
+    if digestAlg == "sha1":
+        # SHA1, this will eventually be deprecated
+        print "sha1"
+        return makeCryptor(hexPrivkey).sign(msg, digest_alg=OpenSSL.digest_ecdsa_sha1)
+    elif digestAlg == "sha256":
+        # SHA256. Eventually this will become the default
+        print "sha256"
+        return makeCryptor(hexPrivkey).sign(msg, digest_alg=OpenSSL.EVP_sha256)
+    else:
+        raise ValueError("Unknown digest algorithm %s" % (digestAlgo))
 # Verifies with hex public key
 def verify(msg,sig,hexPubkey):
     # As mentioned above, we must upgrade gracefully to use SHA256. So