diff --git a/kallithea/model/ssh_key.py b/kallithea/model/ssh_key.py
--- a/kallithea/model/ssh_key.py
+++ b/kallithea/model/ssh_key.py
@@ -21,11 +21,20 @@ SSH key model for Kallithea
 
 import logging
 
+from tg.i18n import ugettext as _
+
+from kallithea.lib.utils2 import safe_str
 from kallithea.model.db import UserSshKeys, User
 from kallithea.model.meta import Session
+from kallithea.lib import ssh
 
 log = logging.getLogger(__name__)
 
+
+class SshKeyModelException(Exception):
+    """Exception raised by SshKeyModel methods to report errors"""
+
+
 class SshKeyModel(object):
 
     def create(self, user, description, public_key):
@@ -33,13 +42,24 @@ class SshKeyModel(object):
         :param user: user or user_id
         :param description: description of SshKey
         :param publickey: public key text
+        Will raise SshKeyModelException on errors
         """
+        try:
+            ssh.parse_pub_key(public_key)
+        except ssh.SshKeyParseError as e:
+            raise SshKeyModelException(_('SSH key %r is invalid: %s') % (safe_str(public_key), e.message))
+
         user = User.guess_instance(user)
 
         new_ssh_key = UserSshKeys()
         new_ssh_key.user_id = user.user_id
         new_ssh_key.description = description
         new_ssh_key.public_key = public_key
+
+        for ssh_key in UserSshKeys.query().filter(UserSshKeys.fingerprint == new_ssh_key.fingerprint).all():
+            raise SshKeyModelException(_('SSH key %s is already used by %s') %
+                                       (new_ssh_key.fingerprint, ssh_key.user.username))
+
         Session().add(new_ssh_key)
 
         return new_ssh_key
@@ -48,6 +68,7 @@ class SshKeyModel(object):
         """
         Deletes given public_key, if user is set it also filters the object for
         deletion by given user.
+        Will raise SshKeyModelException on errors
         """
         ssh_key = UserSshKeys.query().filter(UserSshKeys._public_key == public_key)
 
@@ -56,6 +77,8 @@ class SshKeyModel(object):
             ssh_key = ssh_key.filter(UserSshKeys.user_id == user.user_id)
 
         ssh_key = ssh_key.scalar()
+        if ssh_key is None:
+            raise SshKeyModelException(_('SSH key %r not found') % safe_str(public_key))
         Session().delete(ssh_key)
 
     def get_ssh_keys(self, user):