Crypt/GPG/SubKey.php
public function setCanEncrypt($canEncrypt)
    {
        if ($canEncrypt) {
            $this->_usage |= self::USAGE_ENCRYPT;
        } else {
            $this->_usage &= ~self::USAGE_ENCRYPT;
        }

        return $this;
    }
public function setCanEncrypt($canEncrypt)
    {
        if ($canEncrypt) {
            $this->_usage |= self::USAGE_ENCRYPT;
        } else {
            $this->_usage &= ~self::USAGE_ENCRYPT;
        }

        return $this;
    }
Sets whether or not this sub-key can encrypt data

@param boolean $canEncrypt true if this sub-key can encrypt data and
false if it can not.

@return Crypt_GPG_SubKey the current object, for fluent interface.