synta 0.1.8

ASN.1 parser, decoder, and encoder library with DER/BER support and C FFI
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# PEM and DER Utilities


Two top-level functions handle conversion between PEM and DER byte representations.

## Free functions

| Signature | Returns | Description |
|---|---|---|
| `pem_to_der(data: bytes)` | `list[bytes]` | Decode one or more PEM blocks to DER. Always returns a list (one entry per block); no block present → `ValueError`. |
| `der_to_pem(der: bytes, label: str)` | `bytes` | Wrap DER bytes in a `-----BEGIN {label}-----` / `-----END {label}-----` block. |

## Usage

```python
import synta

# Decode a PEM file with one or more certificates
pem_data = open("bundle.pem", "rb").read()
der_list = synta.pem_to_der(pem_data)   # list[bytes] — one entry per PEM block
for der in der_list:
    cert = synta.Certificate.from_der(der)
    print(cert.subject)

# Single-block PEM (typical for one certificate)
der_list = synta.pem_to_der(open("cert.pem", "rb").read())
cert = synta.Certificate.from_der(der_list[0])

# Wrap DER bytes back into PEM
der = cert.to_der()
pem = synta.der_to_pem(der, "CERTIFICATE")
open("cert.pem", "wb").write(pem)

# Private key PEM
key_der = open("key.der", "rb").read()
pem = synta.der_to_pem(key_der, "PRIVATE KEY")

# Empty PEM raises ValueError
try:
    synta.pem_to_der(b"not pem")
except ValueError as e:
    print(f"No PEM block found: {e}")
```

## Notes

- `pem_to_der` always returns a `list`, even when only one block is present. A single-block
  result is accessed as `result[0]`.
- `pem_to_der` raises `ValueError` when no PEM block is found. It does **not** silently return
  an empty list.
- Malformed base64 inside a PEM block is also rejected with `ValueError`.
- `der_to_pem` produces the standard 64-character line wrap required by RFC 7468.
- The `label` argument to `der_to_pem` appears verbatim between the `BEGIN` / `END` markers
  (e.g. `"CERTIFICATE"`, `"PRIVATE KEY"`, `"CERTIFICATE REQUEST"`).

See also [PKCS Loaders](pkcs-loaders.md) for format-agnostic reading of PEM bundles,
PKCS#7 files, and PKCS#12 archives.