Added loading of DER and PEM encoded private keys

1 files changed, 60 insertions, 0 deletions

diff --git a/rsa/pem.py b/rsa/pem.py
new file mode 100644
index 0000000..a06d59f
--- /dev/null
+++ b/rsa/pem.py
@@ -0,0 +1,60 @@
+'''Functions that load and write PEM-encoded files.'''
+
+import base64
+
+def load_pem(contents, pem_start, pem_end):
+    '''Loads a PEM file.
+
+    Only considers the information between lines "pem_start" and "pem_end". For
+    private keys these are  '-----BEGIN RSA PRIVATE KEY-----' and 
+    '-----END RSA PRIVATE KEY-----'
+
+    @param contents: the contents of the file to interpret
+    @param pem_start: the start marker of the PEM content, such as
+        '-----BEGIN RSA PRIVATE KEY-----'
+    @param pem_end: the end marker of the PEM content, such as
+        '-----END RSA PRIVATE KEY-----'
+
+    @return the base64-decoded content between the start and end markers.
+
+    @raise ValueError: when the content is invalid, for example when the start
+        marker cannot be found.
+
+    '''
+
+    pem_lines = []
+    in_pem_part = False
+
+    for line in contents.split('\n'):
+        line = line.strip()
+
+        # Handle start marker
+        if line == pem_start:
+            if in_pem_part:
+                raise ValueError('Seen start marker "%s" twice' % pem_start)
+
+            in_pem_part = True
+            continue
+
+        # Skip stuff before first marker
+        if not in_pem_part:
+            continue
+
+        # Handle end marker
+        if in_pem_part and line == pem_end:
+            in_pem_part = False
+            break
+
+        pem_lines.append(line)
+
+    # Do some sanity checks
+    if not pem_lines:
+        raise ValueError('No PEM start marker "%s" found' % pem_start)
+
+    if in_pem_part:
+        raise ValueError('No PEM end marker "%s" found' % pem_end)
+
+    # Base64-decode the contents
+    pem = ''.join(pem_lines)
+    return base64.decodestring(pem)
+